Sounds like you have a reasonable set of mics to me. SM57 alone can get a pretty good sound on a guitar. Guitar and amp are, of course, very very important to the overall sound and will probably have a greater impact then any additional mic. Fun to play with other mics though.
For a good bass sound, you might just try getting a good DI box. Sansamp is pretty good. Add some compression and overdrive/distortion and you might just be pretty happy. I've been happy using a Sansamp combined with a D112 mic, but I could probably get by with the direct.
Drums depend a lot on the room they are in. If you're recording in an untreated small room, it will be difficult to get a crisp sound. Also, lousy drum tuning makes for lousy recordings. The mics you have are probably fine for drums, although I've never used the PGs. I assume you just have them on toms and the kick, snare, and overheads will have a much greater effect on your sound than tom mics. Overhead placement is key.
The only thing I see missing from your list is a large diaphragm condenser. These can be used as vocal mics and distance mics for guitars. One idea is an Audio Technica 4033 or 4040. I have a 4033 that is very versatile. Using a SM57 for vocals is ok, but it very much depends on the singer and the style. Condensers are much brighter and can really bring out detail in a good singer. Probably not quite as useful on a screamer.
