And the short answer is, those numbers look fine, I wouldn't upgrade.
If you need to upgrade, it's normally obvious by slow loading web pages. I expect your web pages are loading fine.
Many years ago my numbers were basically idle all the time - anything over 1 or 2% load was rare. Today my server (which does have multiple CPU's) floats at roughly what yours does, and I have no intentions of upgrading - even though the server is probably 5+ years old.