It costs extra though. Also, the Alexa devices can only connect to one account, which would mean one of us would screw up the recs of the other depending on whose account was tied to the Alexa.

If you had a family subscription, you could use one of the accounts just for shared devices. Then you wouldn't have to worry about music played on your Alexa devices messing up your account's recommendations (although it wouldn't count any music played by Alexa devices that you liked either).

You can have two amazon accounts and associate one spotify account with each.