The reason manufactures recommend putting premium in it is to provide the best results and to keep your car from getting carbon build-up on the intake valves which will eventually start suffocating the engine and eventually clog it up to where it stutters.. Since the lower grade is in it, it is less resilient to knocking (not that it will automatically) and it might happen in certain conditions. The car may have over 130,000 miles on it, but you apparently drive it gently.... not trying to BS you... if that problem ever does come up, just go to the O'Reilley's (not autozone... too expensive for cheap stuff) and buy a bottle of Stabil (or whathaveyou) valve cleaner to put in your gas tank to get rid of any build-up and it'll run like new.
You already have 130,000 miles on your Civic??? Unless it's an '03 or '04, that's a lot!!!!