My girlfriend and I went in the end of August, I'm 22 and she's 21. We had a great time! I got that same book, the without kids one... it was eh.
We pretty much did the parks and enjoyed most everything, let the inner kid free a little. We originally thought we'd do the EMH in the mornings, but we slept in too much or got too slow a start usually to do that. If you're staying at the resorts, I suggest to do the evening EMH though, parents are shuffling the kids out and you can actually ride the 2 min rides in Fantasyland that normally have hour long waits and relive your childhood.
I was suprised how many people there were not with kids. Maybe its just the times we went or whatnot, but we stayed at POP and in the mornings only about half the people in line and on the bus had kids.
We usually park hopped in the afternoon around 3/4ish cuz thats when kids are cranky and its the hottest out. We'd go back to the hotel and change, swim, eat, etc... It was nice to swim really late at night when no kids were out either. I found out later that this might be past some of the hotel's swimming times but there were other people there and noone was stopping us.
Sorry if this is digressing into a breakdown of my vacation...
I'd suggest fastpassing things. If you're a couple going there, grab the passes and enjoy looking around, I think I appreciated it much more than when I was a kid. Its fun to shop too, enjoying looking at everything.
Downtown disney likewise was fun shopping. My girlfriend and I have gone to clubs and stuff, but wasn't really impressed with Pleasure Island. We were in the middle of brazillian tourist season and there's something a little weird about club hopping when the stroller patrol is out an about. I'm kinda tall and was a little afraid of punting ankle biters while tipsy, so didn't really do that for too long. That and we went to the Saturday evening mass at the Catholic shrine and there's something weird about clubbing after church...
I'd suggest making a few dinner reservations for places, some nice, and try to go in off times. We went to the Sci-fi drive in at 7:30 on a thursday and it was mostly child proof and then on Sunday we did Coral Reef at 2:00 and that was nice, got a nice meal with a nice view, splurged and got some champagne...
So MK, stay away from fantasy land if you can, except philharmagic which didn't seem too bad. MGM, fastpass stuff. AK, grab fastpasses for Safari, Kali (maybe everest, but wait wasn't bad) and do the 2 animal walks and planet watch, they seemed to be nice and fun, not swarming with people. Epcot is great, snag the fastpasses for the front half of the park, but walk around and enjoy the showcase. We ate and drank around the world, listening to the shows, just relaxing.
You'll find that the inner kid will come out, too, so there's not much difference from the last time you went! Have fun!