case by case
Among my 4 TS, I purchased only 1 title insurance, and it was for Hilton (HGVC). I purchased other 3 TS from the brokers who guaranteed clear title or give refund. HGVC was from an individual seller through ebay, and I am glad that I purchased title insurance for this TS. During closing process, title company found out so many problems from this account, including late MF (2008 maintenance fee was not paid yet), collection company involved, etc...
Closing process was taking longer than I thought, and seller had to sign extra papers to solve this problem. All problem was solved by title company so I didn't have to deal with it, and finally I got a copy of new deed today.
Ask GMAC if they guarantee clean title (or give full refund), and if they don't, and the purchased price is expensive, I would recommend title insurance.