What kind of
changer do you have? I believe Hamiltons are still "pre-wired" to add a
coin acceptor to do what you want, and a lot of older models have the
coin acceptor mounting behind the plastic face. You could even cut the holes yourself with some careful drilling and add a single
coin acceptor to it.
There are many reasons to go "all
tokens," usually to prevent theft. If you haven't had problems with burglary, maybe your option might be to start changing acceptors to take both
tokens and quarters. I've helped a number of people change over from quarters only to a mix of quarters/
tokens in the
changer (usually 75/25) to prevent
changer abuse, and it works. To me it makes more sense than going all
tokens if viewed from the customer standpoint because the ones getting change to use at the wash can use up the
tokens first and take leftover "legal tender" as they're used to doing. As some have said, all-
tokens can be done successfully, but it requires customer
education with which I would prefer not to deal.