"OS security updates are not missing" -- very interesting. How do you get security updates for Ubuntu 10.04? Even the server version was only on life support until April, and is now dead. (The desktop version died two years ago).
FWIW, if I had known about Cinnamon back in the 10.04 days, I would've switched then and there. I actually prefer it over gnome2. But I am in an experimental mood, I'll grant you that.
At the end of the day, if it works, it works. The only real reason to upgrade is for the security updates, and you say you have those... somehow...