I can't sleep at all while in the air. However, if I fly to Europe with a late p.m. departure, I'd upgrade on the outbound. At least I can relax, if not sleep, in a business seat. On the way back, I want to get home so much, it usually does not matter if I am in coach. Just get me home, please! I'll catch up on sleep in my own bed!
However, recently another consideration came to light: on my 2 recent returns, one from FRA and another one from CDG, the check-in was a zoo ! They ignored my status with UA, and made me check in with the rest of the coach passengers. Took an extra 1.5 hrs, causing me to miss all the duty-free shopping. Had I been upgraded to business, the check-in would have been a breeze.
To avoid it next time, I might re-consider my theory of not upgrading on the way back.