I'm not sure why this problem (the general problem - the risk of valid accounts being arbitrarily blocked) isn't an easy fix for google. Most spammers/fraudsters seek efficiency, so just take that efficiency away. When an account is first suspected, start requiring a CAPTCHA for every email sent. Then, when the time comes to block, let there be an annoying but doable automated procedure for unblocking (perhaps involving emails sent from the addresses of several of your frequent contacts), with a time delay - after your first block, it takes 5 hours to unblock, after your second, 1 day, and so on.

It would reduce what is now a very scary prospect for people who (like me) put too many eggs in G's basket, to a minor inconvenience rarely encountered. And I can't see that it would make life much easier for spammers.