Would it affect my car that much?

With a recent tire biting the dust, almost a blowout, I am looking at purchasing some new tires. The ones I have are pieces of crap anyway, about $50 each, and have lasted me long enough to find some new ones.

Currently my stock tires are 215/60R 17. I found a nice set of tires that would work perfectly, but are 215/55R 17. I know the lower AR will make the tires a little wider and the car a little lower, but with that little of a difference make any other difference to the car?

They won't be wider with a lower Aspect Ratio, the Aspect Ratio is basically the height of the sidewalls. In your case, the height of the tires are going from 60% of the width of the tire, to 55%. So, yes they will be slightly shorter (roughly .4" shorter). The 215 is the width of the tire.

But really, your Speedometer will be off a few MPH. Likely 2-3, depending on the MPH you're driving. There are plenty of online tire calculators that will tell you more specifically how off it will be (compared to stock), at certain RPM. Your Odometer will also be slight off, like the Speedometer. Other than that, with such a small change, it's not going to be a big deal. As long as you don't mind having the Speedometer/Odometer off a little, I'd say don't even worry about it.