Oh, I completely know the feeling - I'm just saying (from experience) that you can spend a lot of valuable prep time worrying about stuff that might happen.
For the fighter, there's a lot of options. Again, it depends on what you want to allow. There's a lot of "get 3 spell-like abilities, cast once per day each" feats, and I think there's a good deal you can do with that. If you want fighters to be able to learn magic you can definitely provide feats that do things like "Caster Training: You get 0 0th and 1st level spells, so if you have a bonus from intelligence you can cast first a level spell once a day"
Just like with Gestalt characters, characters with abilities outside their role aren't much more powerful than core characters because the most valuable thing in the game is actions, and the most effective way to spend that action is to find an opportunity to do the thing you do best.
In my experience, players hit 6th level, grab a few feats that really make them shine, and then start seeing opportunities for taking roleplaying feats. An example would be a player who had a wizard taking Martial Weapon Proficiency (longsword) - because he was knighted and given a sword as a symbol of that honor. Once players absorb the fact that the power level is more controlled, they realize they don't need to rush to tweak every tiny piece of their character. At least, that's my take.
