I have an EE with 8 SS bays next
door. The EE had been a FS wash for over 30 years.
As soon as I turned the FSCW to an EE my volume at the SS DROPPED between 40- 60% any given month.
I do believe that having SS bays can be good but how many is the question.
If you really want to keep the all the bays I would make sure you have CC readers/Bill acceptors, dryers, triple foam, etc. in all the bays.
Vend out
tokens at a discount and/or use unlimited wash options.
Otherwise you should consider other options such as Dog Wash bays, Express Detail, maybe even a laundry mat, etc. to draw customers to your site.