If you like exploring and discovering things, then Tom Sawyers Island is your place
Personally, I love it. The raft ride over is fun and a unique experience. I could write pages about the fun times to be had at this place.
Ultimately, it's as long or short of a visit as you make of it. You can spend an hour in the fort, or you could walk through and see it all in 5 mins. The same goes for any other part of the island.
If you're interested in photography, there are definately some cool non-conventional angles from TSI
Dakotadogy:
1 - I sure hope not as well. I believe that there were rumors at one point of turning TSI into something else or replacing a portion of it with the infamous Geyser Mountain, but I don't think that ever materialized
2 - I believe that this secret room does exist. If I'm not mistaken, it's in Injun Joe's cave where you go over the bridge.