Mark, I've done the same thing. If it's less than $50 even if it's in my favor I likely won't file an amended return; if I owe the IRS $50 or less I'll wait and let them bill me.
I'd rather file an amended return than an extension; for one reason, the chances are that it's a de minimus amount anyway, and the IRS won't even bother. Second it takes roughly the same amount of effort to do either one, and I'd just as soon get the process over and done with, for another couple reasons: First, if I'm due a refund I want to get it ASAP. Second, if I owe I want to know an approximation so I can figure out the quarterly payments, if any, and third, I don't want to pay any interest for late filings.