By itself? just bragging rights on here, but coupled with the $100 difference and it creates value. A cheaper console that's more powerful, with a cheaper paid PS plus plan which gives more discounts, incentives, "free" games etc. Put the pieces together and the console puzzle is a better value, which is likely why pre-orders are in PS4's favor atm.
From my own experience, the only thing PS + gives you over XBl is the game rental. XBl is always having some type of sale or discount on items just like PS+ so I do not see a difference there. The price for PS+ is the same as XBL ( just did a general check and both are being sold at 50 bucks standard pricing). I have found 12 months of XBL for 39.99 and PS+ for 44 but I am sure if people shop around they can find it cheaper for both.
I will say the PS+ gives Sony the leg up expecially if you are a vita owner(2) like myself. It would be interesting if MS develop a counter for the rental piece.
My problem with the more power part is that you need to see and feel it in order for it to make a difference. If the X1 and PS4 will have locked 1080P/30 games, we might not see a lot of difference between the 2. Most games will be locked so if one is running 50 while the other is running 40 it will not make a difference to the user.