The points made above are good ones, to be sure, but everyone has his or her own needs, values and priorities, and those often change over time. At an earlier stage in life, I was willing to trek out to Morristown and Greenwich on the train (I’m a carless NYer) for Hyatt MRs, but nowadays I put a higher premium on ease and convenience, so I value my Classic Marriott VIsa and the Ambassador status it helps me retain. It also frees me to stay at hotels other than Marriotts when they are a better choice by virtue of location, quality or price. So no matter the UG offer, I plan to keep it and put my spend on it unless and until I get so disgusted with Marriott that I no longer care about keeping status there.
As for the Amex Bonvoy f/k/a SPG card, it now lives in my sock drawer equivalent, but I’ve derived sufficient value from the free night (around a $300 room rate) to warrant keeping it; it’s also one of my older cards, so I suppose helps my credit rating, though I would not pay an AF just for that. Whether the introduction of peak pricing changes that remains to be seen; if I find that I can’t get a free night in a hotel I want to stay in on a date that works with my travel plans, I won’t keep it.