The refurbished 256GB Pro is only $50 more (only $10 more if comparing base models). Pretty much worth the extra 2GB RAM tbh, especially since RAM is the limiting factor in iOS/iPadOS support nowadays.
ProMotion, quad speakers and camera are just extra bonuses. Personally don't care much about ProMotion, since I don't really use the Pencil but quad speakers are really nice when watching movies.
64GB Air 4 has gone as low as $499 on sale so more like $110 difference vs refurb 128GB 2020 Pro 11.
Mind, I'm more inclined to get the 2021 Pro than either Air 4 or 2020 Pro. Only reason I still got the Air 4 is because face masks make TouchID far more convenient.