Amex so far has shoved 175k MR (plus at one point 5x dining/groceries for 6 months) in upgrade bonuses at me over two years for upgrading cards to Platinums, even though I carry a Schwab Platinum as a keeper. Who am I to turn down such generosity, even though the return diminishes after one Platinum card, and I promptly downgrade them to Gold or Green a year and a day later?

I find it pretty easy to liquidate Uber and airline credits, FHR is more difficult but not impossible (helps that I travel to places like LAS/BKK/BOM where five stars are relatively cheap), so it makes it a reasonable play.