Congrats on your upccoming 25th anniversary!
Disney could definitely do something special for your anniversary. You can have a cake made. You need to contact one of the Deluxe Resorts, (probably the Grand Floridian). You can even have a nice dinner served at Citricos at the GF.
You could have a fireworks cruise. We did this to welcome our guests before our wedding and I highly reccomend it. We had a private pontoon boat and it cruised around the seven seas lagoon before stopping in front of the Magic Kingom to veiw "Wishes". I think the cost is around $120. You may bring your own drinks, as we had champagne, or you can request Disney to provide food and drinks, (at an additional cost of course).
You can also get these cruises over at Epcot to veiw illuminations if you'd like that better. It is the same price, but Illumination cruises are harder to reserve.
Another idea is to have a photo Session. DH and I plan to do this when we go back for our first anniversary. You can choose to have it at any of the theme parks, or at any of the resorts. If you are interested in this option I can dig out my price sheet and let you know the approximate cost.
Also, "The Breathless" is a Yacht that is used to veiw "Wishes". This runs about $350 I think.
What about having a nice dinner at BoatWrights at Port Orleans Riverside and then taking a Horse Drawn Carriage ride. You can only get these carriage rides at POR and at Wildreness lodge.
You could also do a couples massage and the Tea at the Garden Veiw lounge at the Grand Floridian.
O I am just full of ideas as I am trying to plan some of these same things for DH and I when we go back for our anniversary as well.
I hope these ideas help a bit!