No problem operating w/o the drive at all. :)

Nope, you're just wasting a feature you paid for. Most of my cutting is in hot, humid weather. I use the drive all the time. I prefer the Toro 'Variable Speed' because you can 'feather' the bail for less assistance or slower speed when you want to.

If you don't use the transmission; then it should in theory last longer! But who know? I know that Honda lawn mower transmissions last around 7-12 years.

Self propelled mowers are typically heavier, if you are ambitious enough to push yours go for it. Many can't be pushed unless the drive is at least partially disassembled.