Lately many weddings are having large rehearsal dinners. Couples main worries are that they will feel too similar to each other. There are dozens of ways to make sure the both have their own unique and individual feel.
For the Rehearsal dinner, do not use the same color palettes as the reception.
The Rehearsal dinner should never be more grand than the reception
If possible host both events at different venues
If you are having table assignments at the reception, let people decide where to sit for themselves for the rehearsal dinner
You may want to consider letting the rehearsal dinner have a more fun, jovial atmosphere
Choosing totally different music, perhaps in entire different genre, will also give both the events a very different feel.
You may choose to invite less people to the rehearsal dinner, maybe just family and wedding party. That will definitely give a different and more intimate feel. (although if people have traveled long distances, you should do something for them for the night before, even if it is an after dinner party)
slideshows, or videos may be incorporated at the rehearsal dinner . Some of your guest may enjoy seeing you as were dating each other or even you as children.
Feel free to think outside the box, to create different feels and atmosphere at both events. Just something to keep in mind while planning.