1) The upgrade to the QD driver is a part you can buy and bolt in, it's much quieter.
2) This assumes your bearings are good. If this thing is a lot louder than it used to be the bearings may well be on their way out, and a driver won't fix that.
3) Seems old for a warranty claim, but it doesn't hurt to ask, as above they may well sell one at a discounted price.
4) I don't think they rebuild them there, but it is possible. I've done them with mixed results. Using cheap bearings decreases your odds of success.
5) If you aren't willing to take on the bearing replacement and end up having to pay retail for both a new dry side and a QD driver I would just buy a new one and sell the old one on here as at the price you listed above you'll be ahead vs. buying those two parts, but get a new wet side, warranty, and power supply.