I agree!
I actually just came to search the forum to see if I'm missing the "save this vacation" button. When I was planning the trip I just returned from, I kept several vacation package options saved, that I returned to and kept tweaking until I decided what I wanted. I also put in dates that I knew I would not be going, just to get some ideas on cost based on the season (value/etc), before the 2013 package prices were released. I realized that the price would go up some, but it gave me some idea to just play with dates/resorts/options.
The website changed after I'd made my reservations for the trip we just took, so I hadn't dug deep enough to see that this feature is now gone. Now that I'm back and looking ahead (too far ahead of you ask me, but at least I have something in the works), I am really sad to see that this tool is gone.