Steam cash is a good idea when comparing to normal game bundles that are hit and miss, if it is a game you want.
I have had sticker shock at these new boards too. Given that many B450 boards will support Zen3 I would not even look at the B550's unless you need the newer features. I would imagine that few would.
I guess though if there is any chance another generation beyond Zen3 will support B550 that could change things. To my knowledge Zen 3 will be the last on AM4 or at least on DDR4.
I kinda get the feeling that B550 is becoming more the new board in general. They pretty much support most everything 570 does and don't need active cooling.
One thing for sure, B450 boards are getting much harder to find in stores.