I have a city in ME that I parked since April. Most of my GB's are level 10, and some more (arc is touching the 20).
I kind of like the parking parts of the game much more then the advancing. There are good reasons, IMO, for that:
1. You reach higher effective FP production. With good FP swaps you can add half again of FP to your own original FP production. So its really effective when you park and don't waste FP into tech advances.
2. I can farm GE4 easily (I got the PME troops), and there is a lot of gvg around ME in my guild. So lots of fighting to do.
3. I farm this era nicely using CR HQS bible. Got tons of goods that I switch for advance era goods. Medals for expansions and such.
4. And a small personal dislike - I don't like all the building switching needed when you advance an era. You have to rebuild your city again and again. The buildings get bigger which I can understand the reason behind it, but I don't like it.
I cant see myself leave this era any time soon. But I do tend to suddenly just snap and move. It just take a much longer parking time then most.