Well, going from 14's to 15's is gonna mean you need new tires and not really help too many things too much.
The Ranger's factory intake systems are pretty awesome, so that won't help you much either.
Exhausts are always fun to do. If you can come up with something for that I'd do it.
As for spark and timing, spark system is also pretty good, and timing on your truck isn't adjustable, not that I'd recommend timing as a mod. That would probably cause more problems than anything else.
Take a look around the forum. Particularly comb through some of the build threads to see what some guys are doing. When I first signed up I have only the vaguest of ideas about what I wanted to do with my truck. I started combing build threads and the library to see what had been done and came up with my final vision which is still in flux.
Newer badges and lighting stuff seem to be relatively cheap mods that a lot of guys do to make their trucks stand out.