TH8 is worth maxing, since it is the last easy TH to max. After that you will have to pour endless hours on wall farming, upgrades become costlier and longer, and your matchmaking will inherently be more difficult. TH8s can raid TH7-9 players, with premmie- and semi-decent TH9s actually being raidable, as opposed to crappy TH10 bases with central discos - just having those disco ITs make a premmie TH10 quite solid for farming purposes.
So I'd say max away, you probably won't max another TH level, unless you're really dedicated. Your maxed TH8 will also hold up better when moving up to TH9 or 10, and you will have less work to do when you move to your new TH if you maxed everything previously. You will get targeted by TH10s a LOT more when you're TH9, be prepared for that!
