I can definitely sympathize with many of your points. I'm a pretty small guy, so the extra room in FC doesn't really benefit me much, but the only time I regretted getting upgraded was on a red-eye to JFK when I got seated next to a guy in FC that had an incredibly awful bout of gas. I also find that the first class seats are typically much more worn (since they are always filled) compared to economy, especially the fresh, new economy comfort seats on Delta. I'm usually too rushed to eat when I am traveling, so I do appreciate the meals and service in FC when I do get upgraded. Usually my meal consists of an emergency energy bar in economy when I realize that I forgot to eat and start starving to death.

I mostly travel for leisure, so the upgrade to a full-size car when it's just me can mean hundreds of dollars in additional gas expenses.