Unlikely that your roller rockers would cause this problem. If the valves were not fully closing, the car would probably not run or just barely run.
More is not necessarily better with boost, but yours sounds low, has it always maxed out at 10psi? I'd start checking there, see if maybe you have vacuum leaks, sticking bypass valve, old worn-out blower, etc.
BTW, WRX's are faster than most ricer kids drive them at the track - the times are highly dependant on driver skill. It's a difficult car to drive well... I doubt I could get a 14.anything in mine! The best stock times I recall seeing were from Car & Driver, they got a 14.2. Like most turbo cars it's pretty easy to do some cheap mods, you can hit 13's for a few hundred bucks, no problem. If it's an STI, watch out, those do low 13's stock.