What if Combat feats offered bigger bonuses for having more combat feats? Training improves training after all...
Following this idea:
Weapon Focus -- +1 to hit with weapon choosen... +1 to hit with weapon choose for every 4 combat feats you have.
Improve Trip -- + 2 to CMB for trip attacks + 1 to CMB for trip attacks for every 2 combat feats you have.
Power Attack/combat expertise -- + 1 to the amount you can transfer for every 3 combat feats you have.
Two weapon fighting -- adds "If you have more than 5 combat feats you can make an attack with your off handed weapon as part of a standard action attack."
Backswing -- if you have more than 6 combat feats you can apply this feat to your second attack in a full attack action... if you have more than 9 combat feats you can apply this feat to every attack in your full attack action
My reasoning is thus:
1. It can benefit everyone... the more you take the more you get from each of them, representing the extra time you are taking in training on combat.
2. If we scale by level it would benefit everyone the same amount. This benefits fighters more since they get the most combat feats (minimum 10).
Seems already provided...
better feats require other feats in a tiered chains
increase in number of feats gained from normal advancement
could easily see your suggestions added as new feats to fill any gaps
unless change certain feats into progressive incremental talents
meaning...
A) automatic improvement every so many levels, and/or
B) improvement each time selected
basing it on number of feats isn't very different the Nth level
based on BAB feels more appropriate for combat feats though
Well again, basing it on feats means that the fighter will definitely gain more benefit than anyone else will from the boosts... BAB means that any full BAB class will get just as much benefit, whereas basing it off level means everyone benefits equally regardless of how combat oriented he/she is.
Also basing it off of combat feats means the player has more control over how much of a benefit they will get at which level. If it is based off of level or BAB all the player can do is wait for it to build. If it is based off feats then the player can decide when and how many to take to get the extra benefits. Yes they still have to wait for their feats to be available but now they have even more of a decision to make when feats come around. Do they take another combat feat gaining more of a bonus, or do they take that none combat feat that provides something else (generally a bigger scaling bonus over time than what combat feats offer now)?