Actually, I was on the phone this morning with a client who was reminiscing about the big difference retrofitting his self-serve wash for an in-bay made to his bottom line. In his case, total sales doubled.
Area requirements for in-bay are very similar to those for conveyor operations.
Feasibility determination requires rational and formal use of information of which is beyond the scale and scope of this venue. However, sanity testing is not.
For example, one attribute of a new business is its ability to support debt. So, one sanity test for new venture is maximum allowable payment (MAP).
MAP = net operating income / 1.5
Assume adding in-bay generates average monthly gross sales $8,000.
MAP = $8,000 X 0.6 / 1.5
MAP = $3,200
$3,200 would be the largest monthly loan payment that sales $8,000 can support and still make financial sense.
Hope this helps.