I tend to keep mine pretty clean, mainly becasue I equate a clean bike with a cared for bike, and I can’t afford to not look after my bikes.
Cleaning is when I spot things that are wrong (Like dinged rims, a snapped stem bolt and a snapped chainstay….) and I’ve seen more then one person turn up for a ride with a bike that’s obviously not been touched for a while and then have to start fixing it at the roadside before they can ride.
Regular cleaning of the drivetrain makes it last longer too, and also makes it easier to clean becasue it’s not caked in weeks-old filth and oil, so a quick brush with some soapy water has it sparking again (This is also the reason I only use light oil on my chain, not sticky stuff: It’s easier to clean)
It has to be said I’ve never had the slightest problem selling any bikes or parts on, either.
I’m not anal about it, and I’ll leave it for a few rides if it’s not dirty, but I wouldn’t leave any of my MTBs caked in thick mud even overnight when 15 mins with a hose and a brush has it clean again
🙂