I totally get it, it's all a question of balance, I guess. An _occasional_ thanks you mail is great. On the other hand, getting pass the 100 stars on a project on github is a big moral boost too, and probably wouldn't feel so great if each one was a mail :)
But actually, I realize both can easily be reconciled : we could send a "thank you" message to projects with low amount of github stars, and just star those which have a high amount. This would both cheer solo dev starting their project and avoid annoying bigger teams on well established projects.
Has anyone ever been annoyed with a thank you email? Compared to the crap/spam/adverts that turns up in our inboxes every single day, a genuine thank you from an actual human being should be fine. And if not, just stick it in the spam folder with everything else. Github stars are utterly meaningless to many.
But actually, I realize both can easily be reconciled : we could send a "thank you" message to projects with low amount of github stars, and just star those which have a high amount. This would both cheer solo dev starting their project and avoid annoying bigger teams on well established projects.