Should mileage on a trainer be considered mileage on the bike? On my road bike, I have an old Cateye odometer and the sensor is in the front wheel. Therefore, when on my trainer, I can pedal away all day long and the odometer doesn't have any mileage added to it since the front wheel doesn't spin.

When I sell my bike someday, I want to be able to say "It has XXXX miles on it." But all the miles I put on it while on the trainer I can't keep track of. Is that negligible or do trainer miles not really count as mileage on the bike?

I recently purchased a Garmin setup where the sensor will be on the rear wheel by the chain stays, which would solve the problem but I just haven't put it on yet.
Most bikes I've looked at (and purchased) via craigslist and other online listings don't usually state miles, just condition. I think most bicycle owners don't have odometers.

The mileage I keep track of is more for my own knowledge and maintenance scheduling. Keeping track of when I change the chain, or how long tires last type of thing.

That said, I won't get another sensor that only works on the front wheel, as I like the feedback (speed, time, mileage, cadence of my workout) when I'm on the trainer.