First car I got to 217K miles before someone pulled out in front of me killing it, current car is on 138K miles.
I'd up your service intervals to 6 or 9K miles for oil, oil filter and air filter (you can make the air filter last longer by giving it a blast with an air compresser). I use an engine cleaner too and drain the fuel filter – I half the interval to swop out the fuel filter.
I drop a redex into the car about every 3k miles – That tank always gives me an ~5-10% increase in mpg and it feel smoother, after that the mpg drops back to ~48 but things still feel better.
How much is in my head about the smoothness I couldn't say but for the 6 yoyos it costs me I'll keep doing it (although I'm getting tempted by that acetone stuff after reading a few places).