I'm planning to use the drooperons to act opposite of the trailing edge: ex. Deflect the TE down and LE up on one wing, do the opposite on the other - this effectively changes the angle of attack of each section. It'll be effective at high speeds but will start to get problematic when the drooperon tends to stall the section by increasing AoA too far. Of course if the wing is unloaded (load factor = C_L = 0; i.e. AoA = constant regardless of airpseed) then it shouldn't matter.The pitching moments you describe sound about right. The pitch down is because of a larger airfoil generated pitching moment similar to what all flaps cause at small deflections, while the pitch up is because of a combination of flow separation and an interaction between the wing and tail and suggests that you're still getting flow separation on the flaps at those deflections and angles of attack. A higher aspect ratio wing with a shorter chord should avoid such large high-speed pitch coupling, while a T-tail could mostly avoid the low-speed pitch coupling but would result in a design that was vulnerable to pitch up and it might not totally eliminate it.
I was also thinking about what you were saying about increasing roll rate using the drooperons, and I think you might see something similar. Flaps (and downwards deflecting ailerons) both increase camber and effective angle of attack (by shifting the chord line) but drooperons decrease effective angle of attack while increasing camber. Therefore, you might see a small decrease in roll rate at low angles of attack by deflecting the drooperons and ailerons together. However, they should definitely help at high angles of attack where they should enhance aileron effectiveness and reduce adverse yaw.
For unloaded roll rate you're looking for the maximum lift coefficient difference between the two wings. When you start to offset that by adding G in the roll you will eventually run into CL_max or CL_min, where it then makes sense to decrease drooperon deflection (or even have it operate in the same direction as the TE) to keep that side from stalling and/or achieve a greater magnitude of CL at that angle of attack.