Rehearsal dinner- how to make it special?

For a wedding my fiancé was in they had a rehearsal dinner pretty similar to what you're describing. They didn't do anything related to the wedding other than having a couple of toasts, but just being in each other's company and everyone being able to mingle and talk about the wedding and other stuff made it special enough. I honestly think people probably won't recognize if you spent more to get decor specific to your theme or colors. The reason you're going to be there is what makes it special enough in my opinion.

I've been to rehearsal dinners that are more formal, and there is more decor, and ones that are super casual with pizza and beer and then the wedding party helped decorate the venue after. I don't think that there's anything wrong with simple. One thing one of my friends did (it was a smaller rehearsal dinner group) was have everyone go around and say how they knew the couple. I've had friends who put tablecloths and a couple vases of flowers they picked up at trader joes that day with a few picture frames with pics of the couples, which is simple to execute.

I would think of maybe some informal toasts. Flowers on the table would be cool, and maybe pour some bubbly to start the evening off.