I have got to say, this is actually a good thing about WoW and other MMOs. They show us the level of content one should expect from a monthly paid service. If you combined all of the poll items, it still wouldnt be enough content, even if you dropped the price.
I mean hypothetically you could justify making a shooter a stand alone paid service if you added together the poll list in one bundle, plus added Char customization options, multiple series of different gear, such as weapon, armors, gadgets (traps, Heavy artiliry, ect) Then add in series of maps for training missions that could be run offline or on and have an extensive variety of them to choose from of varying degrees of difficulty. A centralized lobby system allowing you to buy sell and upgrade...
Seriously you know what, So much would have to be added in order to justify a monthly sub fee you would have to create an entirely new game from ground up. So unless your willing to put forth that much content developers, dont even bother thinking about an additional sub fee. You will only be shooting yourself in the foot.