This quandary is one reason I chose the UA Select Visa back in fall 2009 when they did their refresh back then* -- particularly as an infrequent flyer, I figure the miles will always have use/value (no jokes about devaluation!), whereas "perks" cards are literally useless if you never fly UA, or fly little enough that those elite level bonuses and "level ups" don't kick in for you. To me, having those tasty category bonuses on the Select card outweighed that small loss of not having automatic priority boarding and all that jazz.
So, even though I am still UA captive in that sense, as opposed to UR that could be transferred elsewhere, it seemed like the best game theory approach to me given the unlikelihood that I would be flying enough to make the elite bonus aspects useful, and of course the above commentary that those are only marginal bumps anyway and don't get you Platinum.
Speaking of which, does UA have an equivalent to the DL Amex deal where you can buy your way to higher elite status through CC spend? I haven't paid as close attention to later UA CC offers, but I feel like that remains a unique DL perk.
*=Forgive my foggy memory, but IIRC it was something like the Select as the category bonuses card (honestly still great unless you have something like the Sapphire Reserve), the Access card basically all the "priority" stuff attached but only 2x UA purchases as category bonus, and I believe the Club Card. I noticed the Awards card pop up over the years, but it seems like one of those "downgrade" cards rather than one they really marketed direct to new applicants (may be wrong on that).