Watch out, I get razzed for replacing oil pressure switches, vtec assemblies and gaskets for no obvious reason. We're suppose to let it fail 1st. LolMy MPG started declining before the CEL came on for a bad oil pressure switch sensor - front bank. I replaced both sensors -- front & rear -- for good measure and my MPG went up again. These sensors play a role in the VCM system (whose whole point is to optimize MPG). My theory is that as the one sensor gradually started failing, VCM wasn't working as efficiently as it should've.
I know you bought the car used but if those sensors haven't been changed at 150k miles, it's time.