I like to equate the reward in miles to how far I'd have to fly for the same reward, and how much that ticket would cost me. So in BMI Diamond Club I'd have to go to LHR and back (from GLA, my home airport) for 600 miles (300 each way on low economy ticket) which costs roughly £100 GBP. So if I can get 600 miles for an activity, and assuming that I want to continue collecting as many miles as possible, it's equivalent to being paid £100.

Agree with the #3 sentiment though, that it is really a hobby and if I was seriously equating it all to money, I certainly wouldn't be wasting my time doing test drives!