I don't draw a difference between Plate Mail +3 and a Cloak of Displacement, both have the same basic problem. When you specialize in defense, you pick plate mail. It limits you in terms of mobility, armor check penalty and dexterity, in exchange for increased defense. Or you pick a shield, dedicating your off hand to defense and eliminating the option for two weapons or two handing. Both require proficiencies.
These choices are true tradeoffs, which can be enforced to take from the same capabilities and you don't really need to alter the exchange rates any further. Due to how the d20 works, a gap of 5 points is going to be the same difference in probability over 20 levels. When you make a tradeoff, it should be between comparable factors. A bonus to combat should cost you in terms of other combat capabilities. Wealth is an uncontained tradeoff. It freely equates diplomacy, information ability, mobility, combat, and all into one single pool, and naturally the most optimal route would always be to spend on the area which you can be sure will turn up(namely, combat).
Feats don't vary game by game, treasure often does, in spite of the necessity. WBL is a tricky thing to keep in the right range, when for the most part there just isn't a NEED for such number wrangling and huge treasure amounts.