A while ago I bought an SM57 and loved it. However Guitar Center advertised a deal to buy an Audix i5 and get a free boom mic stand and XLR cable. I had bought all that along with my SM57, so this deal interested me. Even after returning the stand and cable though, I couldn't afford two mics at the time, so returned the SM57 and bought the i5, since, at the time I figured every mic sounded the same and just captured audio, a mindstate I'm thankfully no longer in. It works well for acoustics and vocals, but it sounds awful for anything with the word gain added to it.

So, I've been considering buying another SM57. I'd prefer not to spend the cash since I almost have enough for a computer for recording that I've been setting money aside for that was the reason I couldn't afford two mics in the first place, and after that I intend to buy a wah I actually like, but at the same time Id like to start getting some recording done

Although up until now my only two ways of hearing what the mic hears have been a crappy pair of $10 earbuds(Soon to be replaced with a pair of studio-quality Sennheisers,) or my computer's speakers(Soon to be replaced with a set of JBL monitors after the new computer), so there's a good chance the sound was being coloured fairly poorly by them. Would I be better off waiting until after I get the headphones and/or monitors to decide whether or not to buy another SM57, or should I just go out and put down for one?

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since you already have a mic that works well enough, i'd wait till you get the rest of that stuff. a second mic isn't as important as a decent comp or monitors.
A new mic is useless if you can't hear what it is recording.

Upgrade monitoring setup , then get a SM57