a good sound system will tend to amplify some of the shortcomings of mp3s, especially the dodgier ones. it's always a good rule of thumb to use wavs when you can, whether it's in dj'ing, making mixes, etc. (as long as they're original wavs and not just mp3s converted to wav.)
as for your opening track, the noise reduction plugin in sound forge is very good at cleaning up a noise that runs constantly through a track, such as tape hiss or a noisy stylus on a vinyl-to-digital recording, or even the hum of an air conditioner in the studio. you capture a sample of the noise during a quiet part in the song where only that noise exists (often at the very beginning or end), then the program will remove that sound from the entire recording. i used it on an al jolson record from 1924 just last night, and it worked very well. be careful not to overdo it, as if you reduce the noise too much it can leave artifacts on the rest of the audio.
if you don't have sound forge and the noise reduction plugin, or anything similar, don't despair. a recording from 1929 *should* sound like a recording from 1929, and as long as it's not some 10-minute thing that would wear people down before it's over, it can be a nice effect to segue from something old and "grainy" into something fresh and clean
as for playing between bands, be ready for the upcoming band to make a lot of noise tuning up, etc., while you're doing your art. just shoot them mean looks and then refuse to quit playing records when it's time for them to start
