Let’s say that you need less than 5k vouchers to upgrade a high-level module, and you don’t feel like going on a lower rank, but you gain like 20k vouchers a game(with premiums and all), 15k would just be wasted, instead of being transferred to the next level of upgrade, it would definitely be a useful little feature that would spare us a few battles, I mean, look at this:
I basically earned three times as many vouchers required for the upgrade yet I spend only 2.5k and the rest just vanish, instead of being used for the upgrade from mk3 to mk4.
About upgrading mk4 and having extra vouchers, they could go to the free vouchers with a penalty, although playing other games with nothing on the research would yield no vouchers whatsoever as it still does, we already have more than one thousand unique modules to upgrade, let’s not talk about getting duplicates.