It's not logical that PS+ will lose quality imo. The more popular the PS4 gets, and the more games there are on it (right now over 500 different development studios working on it), the more likely it is free games will be on there. Also, textures more revenue Sony make from it the better the content (see Euro PS+ vs US PS+). At the end of the day, if the market is crowded, some revenue via PS+ downloads is better to a developer than getting lost in the mix, selling hardly anything and getting even less revenue, namely for indies. At least they get some coverage and sales as a result.
My guess? PS+ on PS4 will be even better than it has been on the PS3. Resogun and DriveClub day one is certainly positive.