Are you an active player and do you intend to run a few raids each day? If so, then upgrade; it's the natural progression of the game. You will spemd 6-9 months at TH8, running upgrades and learning new strategies. If you like doing clan wars, upgrading is also a no brainer. TH7 is the first level where you can effectively compete. Of course, it's also a guaranteed three star in every clan war. But, it is a good place to really start learning the art of air attacks. TH8, however, opens the door to a bunch of other attacks with the introduction of the PEKKA and golem.
I have THs at 6, 7, 8, 9, and 11. I will keep a couple at TH7 just for clan wars and to free up my time to work on my TH9 and TH8 games. Once those are maxed out, I will probably go back and convert my TH7s up to TH8 as well.