I notice you're syncing tasks every minute. Perhaps a short-term workaround is to sync every 2 or every 5 minutes while you wait for the quota to increase?
This is exactly what you should do. Your users will understand -- that's why so many have supported you on the googlegroup. Charge $3/mo and you won't hear any complaints (and if you do, you can point to your googlegroup).
This is by far your easiest and clearest path to monetization, at least that I can see. And it seems you're long overdue for monetization.
Can you adjust the sync rate depending on the time of day where your users live? There are probably certain times of the day when people update their tasks less frequently.
I'm not sure if it works with the Google API's but usually e.g. with the GitHub API you can send the ETag in your GET request header and if nothing changed (304) it does not count to the quota. It wouldn't solve all the problems but could at least help to stay inside the quota.
I am already doing that, because of that only I am able to survive 2000 users. I want to expand and publicize my app and give users an excellent experience.
I know it sucks, but in the meantime have you considered slowing those sync tasks down if the user's "last activity" timestamp is older than a few minutes? You might even be able to make it sync faster for active users with the extra overhead afforded there.
Logins, refreshes, clicks, new things synced, etc... can all update the last activity timestamp.
You're incredible guys. Why wouldn't you reach out to him first? Guy spend two years f with you and now he also have to screen your blog for your email too.
The sad fact that you, a random HN commentor, likely has a better means to contact Google than their official Dev channels, perfectly illustrates the OP's point.
Kudos for assisting, its just frustrating to realize its needed.