Welcome to the forum, Chase. Yeah, there's a LOT of difference between an older SG and an new RGU. If you buy the SG, you're buying a hot rod from someone and you really can't be sure how it was driven, but they didn't but a bigger engine in it to drive it slower. Plus with the SG, you'll be spending a lot of money bringing it up to were you were talking about with rear speakers and a tour pack.
Are the new RGU's worth the money? There are those who'll say no, even if they own one. Heck, I've got a '15 (and that might be a good one to consider if you could find one), but they're expensive. Too much so in my book, but I love mine.
Tough call.
Do some reading and research here on the forum. Maybe it'll help you decide.
Welcome aboard in the meantime!