I asked a similar things about hotels and was told more than one status is dumb, etc, etc. But in reality other than rollover once you hit Diamond there isn't much added benefit. Having flown many airlines in the US, I personally still am more comfortable with IRROPS and seats/treatment with Delta but that's me.
You're aware of the new UA changes? I've been eyeing them based on a potential move, and the new changes ... well, change things.