Aloha,
We have often done one day trips during the off-season and we were able to see most of the shows and ride some of the rides. But we always had kids with us. Last year, we did an adults only trip - but stupidily scheduled it during spring break and we were able to ride everything but unable to see any shows. We spent more time in lines than anything. So I think, if you go in the off season, two adults should be able to do most if not all if they push it a little. If you go, be sure to see their stunt show. Over the years, we have seen three, Conan, Miami Vice and the current Waterworld. They are usually action filled and very impressive. I suspect they are very expensive sets to produce and that is why they don't change annually. Sometimes USH staff post here, they may be able to help you more.