a cold air does nothing more than make noise. a k&n panel filter will net the same power increase and you'll spend $200 less.
Replace the timing belt assembly first and foremost. If that belt breaks and pistons kiss valves, your $400-$600 in parts/labor preventative turns into $1200+ easily. Thats your call. AND if the head ends up getting crack in the process, tracking a head is harder than you think. These aren't hondas...
Since you're in the Nazi-anti-mod state, aka CA, a tune is your next "power" mod. Beyond that, poly motor mount (or $25 for poly bushing replacement) and replace your shocks/struts.