I would move to SQL_CE, it is file based, all you need to do would be to change out the web.config, use the one under SQL_BE in the setup file and follow the easy instructions to setup the database.
I use it on my hiking website with several hundred users, it works great, I used to use Vista Express and I think SQL_CE is faster. I reentered several hundred new users when I changed over.
You will have to renter the users which is not an issue it goes very quickly. I changed the password to clear to hashed to help some users that have an issue with reseting their password.
Be sure to setup any roles first so that when you enter the users you can select the role you desire.