When purchasing Music (£0.99 each) how many plays would you say made the purchase 'worth it'?

That's a big motivation for me, too, but I'd say it's about equally that I want archival of the best stuff for when rights holders pull their catalogs from the services I stream. I used to think that was mainly for the more obscure stuff, like local bands' early albums that I can barely find anymore, but recently I've noticed albums missing from main services (Tidal and Spotify, in my case) for bigger acts, too.