I'm not sure how disposable card numbers help. If you buy an app, a track, a film, a tablet from Google Play, that purchase is linked to the account, not the card. How is your account then disposable? Surely it's better to have an account that you use for your purchases, which you protect strongly, than run the risk of losing access to.purchases or returns.
I can understand having additional disposable accounts, but it makes sense to have a main account which you protect as strongly as the tools allow you to