I didn't read all the posts but I went to TH9 with a completely maxed base except BK LV8 and I didn't touch any dark troop in lab. I don't know if I would have maxed TH8 (especially walls) pre update, I farmed those skulls with elixir and gold, took me around 2-3 weeks.
I'm a TH10 now, came from a maxed TH10 (except valkyries in lab, 15/15 heroes) with full legos and many told me to max everything, but I moved to TH10 and I dont regret my decision.
I'd say upgrade whenever you feel comfortable with it.

