I have a Folger 2020 i3 not a Wanhao - but they're both i3 derived designs so very similar. My stock hotend was a Mk8 not a Mk10 but again the changes between them are minor.
I upgraded from the MK8 style extruder/hotend to a E3D v6 hot end with a 3D printed extruder with a few of my own modifications done to it. There are plusses and minuses to the upgrade. My primary reason for upgrading was I wanted an all metal hot end so I could use more exotic filaments that require higher temps. I do a LOT of PETG and found that it works best at the upper limits of what a teflon lined hot end can handle. I even melted my liner at one point pushing things - you don't want to deal with that! I also wanted to be able to print Nylon and other materials that are even stronger but require temps that teflon liners can't deal with.
I picked an extruder based on what would be easy to adapt to my printer, would be direct drive (I didn't want to deal with gears or belts), and would have a well constrained filament path so I could also do flexible filaments well.
Overall I was able to get just as good of print quality (and in some cases better) with the with MK8 than I am with the current setup. But the new setup has opened up a variety of material options which I greatly enjoy.
I did do an intermediate upgrade from the stock plastic Mk8 to an aluminum version I got off ebay for $12. That helped improve print quality a LOT because it provided more consistent and adjustable pressure on the feed idler:
I would have been very happy to stay with that extruder (at least until I started doing flexible filament) and just swap to the e3d hotend...but there was no good way to mount an e3d to the metal extruder.
So I went with this extruder to match the e3d:
http://www.thingiverse.com/thing:825133
I added two of my own upgrades to it:
An improved idler that has a tab on it so it's easier to release when changing filament:
http://www.thingiverse.com/thing:1427181
An inductive sensor and layer fan mount:
http://www.thingiverse.com/thing:1449709
Note - while I printed most of the extruder in PETG (I eventually want to enclose my printer for doing ABS and worried about PLA holding up to the temps) I did do the idler in PLA because I wanted it to be stiffer. I also did the sensor mount and fan in ABS because without a fan ABS was easier to print than PETG and I was worried about PLA holding up that close to the heated bed and hot end.
I also upgraded the teflon tube on the extruder since that photo by slightly lengthening it and trimming it into an inverted V at the top so the filament is fully constrained as soon as it leaves the drive gear. I've done a good bit of TPU flexible filament now and only once did I have an issue with it getting out of hand when I turned up retraction too high.
I've since printed a wades style geared extruder as printing with maker geeks PLA I was having issues that seemed to indicate I needed more drive force on my filament. I haven't installed that extruder yet though as I've yet to come up with a good way to mount a layer fan and my inductive sensor to it. And I've since solved the issue the maker geeks PLA was giving me by using a tiny clothespin to hold a bit of paper towel with a few drops of vegetable oil on it over the filament just before it enters the extruder. I've only had to do that with the MG PLA, no other filament I've used has had that issue. Not sure if it's because of the all metal extruder or just something about MG's PLA but I've heard it's fairly common with their PLA. (Note: their PLA is kind of odd and likes much higher temps than most....the roll of white I just got they recommend 235c! But at $15 a roll delivered when you buy their grab bag and don't care about color, or in their monthly maker box it's a killer deal.)
So - the "upgraded" hot end and extruder has widened my printing ability...but I wouldn't say it improved my quality any. Dialing in my slicer did far more to improve quality. And that's where I have an issue with 3dlab prints.
I really want to print one of their planes. But I've yet to get a usable print of any of their demo files.
The issue is I use slic3r and their designs don't slice in slic3r for some reason. All the internal structure gets lost.
I've tried CURA several times (with both hot end/ extruder setups) but can't get decent prints with it and get frustrated with it as a result.
The big issue is I use single wall prints to dial in my slicer. The logic is it's the best way to make sure things are going to do exactly what you expect and be dimensionally accurate. Most of my printing is functional parts not decorative stuff so I want the most accurate parts I can get. I use a
20x20 hollow topless/bottomless test cube designed with a 0.48mm wall thickness to test. I print with a 0.4mm nozzle which means 0.48 is the ideal width for a single wall extrusion. The plastic expands as it comes out of the nozzle, so you usually want to print with an extrusion width that's 120% larger than your nozzle size, if you want a different thickness you should run a different sized nozzle. And if you run a different sized nozzle you'd want to aim for a different sized thickness.
The basic writeup on the calibrations I do are here:
http://northwoods3d.weebly.com/blog/filament-calibration-part-1
http://northwoods3d.weebly.com/blog/-flow-rate-how-much-plastic-is-coming-out
I don't agree with everything on her blog, but her filament calibrations are one of the best write-ups I've seen of the method.
The problem is this doesn't work in CURA. If I try to slice that test cube in cura - I get an empty file. It ignores the single wall thickness!
This is why 3dlabprints confuses me...with a part designed for single wall printing cura ignores it but slic3r does great. But with 3dlabprints stl's the opposite is the case and cura will slice them but slic3r chokes on them. So I have a really hard time getting CURA to do accurate prints because I can't get it to slide single wall test pieces to confirm that I'm extruding the amount of filament I'm asking for.
As for simplify3D...I can't justify spending more on slicer software than I did on my printer when I can get such great results on everything except 3dlabprints designs with slic3r which is free and open.
With the calibration method I used I can print the Make 2015 shootout tests pretty much perfectly:
http://www.thingiverse.com/thing:533472 Specifically on the negative space tolerance test I can remove all of the pins (though the tightest one does leave a dent in my finger from the pressure required to get it out.) I can print all kinds of print in place designs with no issues and get extremely accurate dimensions on my prints. The error from my $15 harbor freight calibers is larger than the error from my printer at this point
I plan to spend more time with cura wrestling it into submission so I can do one of the 3dlabs planes at some point...but my project list is pretty long already
Back to the original topic. I don't think a new extruder would give an increase in quality like you're hoping for. More time spent calibrating and dialing in your slicing software is more likely to achieve that goal in my experience. Though I'm still struggling with just how to achieve that in Cura.
(FWIW the biggest issue I have with cura is that the same designs that print fine for me in slic3r refuse to stick to the bed when I slice them with cura?! Which makes no sense to me as the settings are pretty much the same and I can't see anything about the gcode that would indicate the first layer should be any worse. Honestly I think cura is just cursed for me
)