I like this idea a lot, it might become my new head cannon!

Possibly. But how much more wear & tear would this be compared to the wear put on the warp drive, which gets incredibly frequent use? If that warp drive can withstand it, why not the shield emitters?

Yeah, I think the power-saving argument (#4) is potentially strongest, especially if the plot needs it to be for a given episode.

But I’m having trouble thinking of a situation in the shows where the maneuverability was limited by the shields. Certainly there are plenty of cases where power was routed to shields, maybe even the power that was meant for propulsion. But I think in general, those would be cases where power was already limited, or the need for defense was much higher. In general, I don’t think I recall a trade-off where shields restrict maneuverability or speed.