i've been contemplating the idea of a spanner-only shop near to the major office complexes in town, with the objective of turning people's bikes around while they are in work...
this would work in the right area. a small stock of consumables & smaller items... tubes, tyres, grips, saddles, brake pads, pumps, helmets etc and more expensive kit bought in to order such as brake sets, shifters & mechs.
the only potential downside with a shop like this would be that you would have to be open for 7.30 / 8 ish in the morning and potentially not finish until 6.30 / 7.00 in the evening depending on the travel times of the local workforce.
there must be a big demand for those who commute to be able to drop their bike off close to work, get those new tyres fitted or wheels re-trued then pick it up on their lunch hour / when they finish. the expansion to include new & second hand sales, rentals & custom build options could make it viable with an online side to the sales as well.