[havelegs]

Probably won't notice that much difference in fuel economy, maybe 1mpg ~.

But, I have read on some Corvette forums that after not using AFM and then going back to it is where they had issues. I would probably keep the Range plugged in but maybe once a month take it out and let AFM activate to keep things in order.

It's not common for the AFM lifters to fail, but not uncommon. It's been known that if you go with long intervals between oil changes, that can increase the risk.