To be honest, your milage doesn't sound too bad especially if you still have a couple of gallons left in a tank and it is mostly in town. That's about what my D16z6 gets if I do almost all in town. Have you figured out what the miles per gallon is? The best I have got was about 405 miles on a tank that was all highway (I was taking it easy to try to get the best mileage I could), but I usually have to fill up every 260 miles or so if I do mostly all in town with some highway.

From what I heard the pcv valve is only a couple of dollars from an auto parts store. It is also easiest to change it at the same time you change your oil (from what I have heard). Never actually have done it myself.

For the injectors, just get some of the stuff you put in the gas tank to start off with.