I generally don't get rid of mics, as I keep thinking that I might find some good use for even a crappy mic, if I just wait for the right opportunity. Heck, I have an old Electrovoice SM58 copy that still gets use occasionally. (I use it for presentations, where my business partner - a clinical psychologist - likes to have a vocal mic with an on/off switch, and the lack of sufficient HF content helps keep it from feeding back. He doesn't know much about audio gear, so it's helpful to keep everything as simple and idiot-proof as possible.)
However, I must say that I once had about 8 SM57's. This was back in the 1970s when EVERYBODY had a half dozen or so of em' lying around. But, the qualtity of PA gear improved, which demanded more accurate mics. And I gradually aquired mics that do a better job on just about anything that you can think of to use an SM57 for. (A Beyer 201 for snare, a sennheiser 421 for guitar amps, etc...) So, I just didn't find them very useful, anymore. I kept two, just in case I find something that they actually sound good on, or if I run out of other mics to use.
One mic that I haven't got rid of YET is the MXL 603s. I've got a matched pair that came free with a Presonus MP20. Since they're free, I really can't bitch too much about them, but I really can't say that I like them very much, either. I realize that many people on this board like these mics, but their sound is just not happening for me. Not only do they boost the highs way too much for my taste, the high freq. content that IS there just doesn't SOUND GOOD to my ears. There is a good chance that they will go bye-bye as soon as I get a pair of decent SDCs, such as the Josephson 42's, or those new Puleso (sp?), or even a couple of good 'ol SM81's. They might be acceptable for some purposes, though, such as live OH's for drums. That is the only application that I've used them for, so far, and the sound man thought they sounded "O.K." Maybe their tonal characteristics will shine in that application, as the extra high freq. might help them cut through the noise of a live concert, and the "harshness" that I hear wouldn't really be noticable. So, I'll have to just wait and see if these become "keepers" or not. But, right now, I'd say there's only about a 40% chance that they'll end up staying in my mic locker.
Brad