The challenge is that the customers you target with a minimum viable product aren’t the same customers who will also pay big money for a full service - so building that customer base is irrelevant.
Perhaps more opinion than evidence but I would expect a lot of the more sustainable detailing businesses (at least in their infancy) are the ones that are catering to the 'casuals' who are happy to spend a few hundred quid to get a decent clean, polish and cheap coating that can fill gaps in the bookings as well as the 3 day multi stage jobs into the thousands.