Cleaner first drafts: should I be happy or worried?

Ergh... I think all that matters is the finished product. As long as the finished product is good, it doesn't matter how you got there.

My two cents.

I find that over the years, my first drafts are cleaner, because I've finally absorbed the corrections to certain errors I used to make regularly. If I start to type the words just, even, really, actually, etc., I know to stop and delete. A lot of other old habits I've broken. Hopefully, what you're experiencing is something similar. You've identified your weak spots and you're learning not to make the same mistakes you used to have to correct.

It's good that your first drafts are getting cleaner. It means you're learning and growing as a writer. You know what your weaknesses were, you developed on them, and you aren't making the same mistakes you used to make.

I think it sounds like a good thing, not something to worry about. As others have said, perhaps it merely means you've improved such that you don't commit as many errors, so of course there isn't as much for you to clean up.

Best of luck.

I think you should be happy. Your writing is probably "cleaner" so your drafts would reflect that. My writing has gotten cleaner since I started paragraph one to the final chapter thirty-one. I've seen a difference. Likely, yours is too. Enjoy the transition! Good luck with your WIP.

Definitely a good thing.

You'll still make mistakes, of course - but less of them.