It might be worth thinking about having a way to train soldiers other than real combat. Obviously simulated fighting isn't a substitute for real experience, and off-duty soldiers shouldn't gain EXP as fast as active ones, but it'd be a neat way to solve the "your heroes got shot, so now you're boned" syndrome.
Maybe just have another base facility that slowly increases soldiers' stats up to a certain point, resetting whenever they gain experience on a mission. That is, they'd get maybe ten points total of "free" stat increase, then they'd have to get an increase from the real thing to reset the counter.
