the combat expertise feat currently sucks and needs to be decoupled from the 3e baggage
1. remove the spell casting penalty, it was never necessary, so what if a caster has 5 more ac, it cost them a feat - if some kind of penalty is absolutely necessary it should be a fixed penalty of say 10 mana extra, having metamagic costs double is absurd
2. remove the int requirement, tank builds who could potentially use the feat don't have the build points to spare, let them have more useful stats, instead couple some CE effects to int
3. make CE (active or passive) give an additional 20% bash chance if you have shield mastery, this would trivially increase the pew pew of all 2 dedicated shield users out there
4. make CE (active or passive) have the following effect: use either int or str, whichever is higher, to determine DC for combat feats - this one change would give it potential for rogues, melee artificers, monkwiz pale masters, and also really fit the theme of the "smart warrior"
5. make CE (when active) add positive int bonus to melee critical hit damage before multiplier, again this would make the feat attractive to rogues and be in line with the "smart warrior" flavor