Here is my proposed action plan:
My wife files for her social security at FRA (she is several months older than I and has less earnings)
I file for spousal benefits on her account when I reach FRA.
When I reach age 70 I file on my account and she files for spousal benefits on my account.... is this legal/feasible?

Yes, this strategy is legal and feasible. Your wife's excess spouse's benefit, which she will receive in addition to her own retirement benefit, at your age 70 will be equal to one half of your full retirement age (FRA) retirement benefit, not your increased benefit, minus her FRA retirement benefit. So, your FRA retirement benefit must be at least twice hers for her to receive an excess spouse's benefit.
Best,
Mike