We did the wine option on our recent visit Feb. 5-9, 2008. It wasn't bad, but we probably wouldn't do it again. Your assumptions are right on. The plan excludes "premium wines". Most of the wine we got were in the 50.00-57.00 price range. So it was definately a savings, however, as mentioned some nights I may have preferred a mixed drink. Also if your sit down dinner was at lunch, you probably wouldn't want a whole bottle of wine. On our last night we had one wine credit leftover so I went to the Outer Rim lounge at the Contemporary and the bartender very graciously opened a bottle for us and gave us glasses to take bak to our room. I wasn't sure if that was possible, but it saved us from using two 2 credits through room service! Also, don't forget, you're tipping on the full price of the wine!
Hope that helps!