If all you care about are the lounges, then there's probably no reason for you to not cancel the card. But since there is no prorated membership fee on USA cards. you might as well hold onto it and see if you are offered a retention bonus when it is time for renewal. Or you could consider trying to downgrade to a Gold card for the remainder of your year.

I have reasons to not get rid of the card; I still use Uber & Saks, I have a December trip through Platinum travel, and it's not even May.

I can understand not applying a face value on those credits, but how much do you value them? What portion of the $550 do you assign as value towards the lounges? My point is that if I think of the credits as being worth $250, I then ask myself if it's worth a cancellation/downgrade over $300, or $25/mo for the months I'm not using the lounge or other credits. To me, the relationship and extended warranty on products purchased in the past 2 years are worth that price for the one year I didn't "make money" on Amex. I also remember that the when the international airline program was BOGO, I saved $4000 ($7000 face value, but I compare to what two non-ref biz tickets would have cost) on a trip to Australia.