A useful service could be N washes per year with a minimum interval. The user chooses N. Out of this a fraction would be "on-demand". The others would be optimized for availability of resources like manpower and suitable places where there is no objection to washing. For Eg. the user can indicate some travel patterns which can help identify optimal schedules. This approach will enable the user to have a generally clean car and summon a cleanup when there is a special occasion. Such a subscription service would charge lesser per wash.