Well, it's certainly enough time to do the Ramada (which you can bet has much nicer showers than any of the lounges; incidentally, I don't know of any lounges that have showers, but if there are some, I'd be willing to bet that they are nothing special).

As far as going into town is concerned, let's run the numbers. For the sake of simplicity, I'm going to assume a noon arrival, a 340p departure and that the luggage gets through checked.

-1240 Maglev arrives at Longyang Rd at 1248
-Subway to Lujiazui, arrive by 110
-1 hour to check out the Binjiang Park and maybe the aquarium brings us to 215 or so
-Get back to Longyang Rd in time for 240 Maglev, which means you'd really want to be on the subway by 220; the 3p Maglev will also work, provided the OP is a fast walker, but I certainly wouldn't plan on taking that train

Now, while the above certainly isn't my idea of fun, it still affords an hour of touring time; plus, the Maglev itself is also interesting/fun. Furthermore, in the event the OP arrives early, the 1220 Maglev might become an option.