I actually bought a Line6 Toneport for this very reason. I kept running into bands with godawful amps (crate are the worst, followed by some of the open back solid state Fenders). Now, if I can't get a good tone in 15 minutes, I take a DI to a separate track, and reamp it through the Toneport later.
The toneport doesn't have great tones, but it smokes a Crate! And you can reamp the same guitar signal to two or three setups, to get a nice big stereo sound.
If they're playing through a decent rig, I use a 57 or an e609, close enough to get the tone, but backed off until the mic stops breaking up (I hear mics being overdriven a lot, sounds awful. Put your finger in your ear and listen to the playback. If you hear that high frequency grind, that's the mic being overdriven, usually).
Watch for comb filtering, get small amps up off the floor, if you're micing a 4x12, use one of the upper speakers, again be aware that your mic will be picking up the sound from multiple speakers, especially if you back it off a foot or so.
Lastly, I don't eq or compress while tracking, but during mixdown, I run the guitars through a tape-sim plug, with medium saturation, and I might add a little eq at 1500hz or so, if I want the guitars to be a little edgier.
