I would think that there's one caveat though and that's probably that up till about a 90/10 mix you will be limited by the worst properties of both fuels.
I have no specific experience with mogas/avgas, but the Diamond I fly is certified for both Jet-A and Diesel fuel. However, when it comes to cold starting/cold weather operating, even with a 90% Jet-A, 10% Diesel mixture you've got to apply the temperature limits as if you are flying 100% Diesel.
I would guess you would find more or less the same thing with, for instance, vapour lock. If there are specific (altitude?) limits when using mogas because of vapour lock, you'll probably find that they apply as well to a 75-90% avgas, 25-10% mogas mixture, or something along those lines.