So how cool would it be to be able to have an option on whether or not we want to use rested exp? It would be simple. Rested xp recharges at the exact same rate that it does now, but there would be an option to turn it on or off, so that when it is on, any exp you attain is boosted with the bonus, and if it's off, you don't.

This wouldn't really break anything, as ultimately, you are just saving your rest exp for a job you'd rather use it on, or amassing a full bonus to use on a day you have a long time to play. Any exp earned with the bonus turned off is just normal experience anyway, so I don't see the harm in it.