Is it frowned upon to revive old questions if it's not that important? I keep finding really old questions that I could answer, but most of the time my answer is rather trivial and it feels silly to bring it all the way to the first page.
As long as you're not trying to game the Necromancer badge* and have good information to add to the original question, I'd say this is actually preferable. People looking for answers to questions (ought to) turn to the existing questions first before posting their own, so it's beneficial to have a question gain better answers, even long after it was originally asked.
*By gaming, I mean using worthless answers to try to grab it. I'm okay if you're trying to get the badge but actually have something of substance to add.
Your answer might be trivial to you, but if the question does not have a selected answer, then what you have to say could be very valuable to the person who posed the question, and if not them, someone searching and READING the question...
I've answered questions that are MONTHS old, and still got accepted answers.
Or, maybe you shouldn't.. Give someone like me a chance to answer... heh... Just kidding..
I really think that if you have something to add to the question, or the information presented in the thread, you SHOULD in fact answer. Even if people got the answer, but didn't MARK it, someone else might come along and read your answer and get valuable information out of it... I know I would.