That seems like a pretty good and different idea. It also shouldn't hurt the wallet much.
I was thinking, I did at one point contact Gifts of a Lifetime. What there service is is that you answer a bunch of questions about your hopefully soon to be fiancee and they come up with a couple of different "Events" for her to do either in the parks or at a resort. You can then work with them on tweeking the event (they told me they can arrange a Photopass photographer to be there at the end of her Event when the proposal happens). The events sounded interesting and fun (they do cost a couple hundred bucks) but it would deffinately be more on the unique side. You don't have to commit to anything, so I would look into it and at least get a few of their ideas and prices. You have the time and it doesn't cost anything, so why not, right? I just decided not to go with them because I decided I wanted to do something a little more private since my fiancee is not the "center of attention type". Just keep in mind that they have no affiliation with Disney. The site is:
http://www.giftsofalifetime.com/
Also, if you are looking to do something more private in your room (which is what I ended up doing), Betsy from Memories By Betsy did a great basket and bouquet of flowers for me. Amongst other things, the final part of the basket was a 5" glass slipper that said "Let's Life Happily Ever After" on it. It was really nice and my fiancee wants to engrave the wedding date on it after we get married. She was really easy to work with, unlike Disney Florist who was tough to hear back from and who could not really personalize any of their packages. Betsy's site is:
http://www.memoriesbybetsy.com .
The only other thing I would suggest is to propose early in the trip. You don't want your mind to be elsewhere the whole trip. It also gives you a chance to use more of the trip as a celebration. The "Just Engaged" pins are a lot of fun to wear. The characters really get into it when they see them and any CM you pass is very quick with a "Congratulations". However, don't note the engagement on any reservations until after the deed is done. I have heard stories about resorts ruining the surprise for some, which would be a bad thing.