Indonesia
I've played multiple times. I find them fun, but a little too strong in that I don't have much trouble winning with them on Emperor (although I've only just gone back to my pre-BNW difficulty, Immortal, and not with Indonesia).
Morocco
While Morocco looks strong on paper, and my experience in practice is that they're somewhat less so (highly dependent on early placement with multiple accessible trading partners, a desert UI with no desert start bias, and little to no evidence from my experience that AI civs preferentially trade with them with the gold bonus), I do enjoy playing them somewhat. When you get the right start, that early culture can even be meaningful although it invites comparisons with "Old France" and comes up short in that comparison; what it's not going to do is make you a difficult conquest for culture victory. Unfortunately my last - and most advanced - Morocco game suffered an apparently irretrievable crash, with the game crashing at the same point regardless of which saved game I start from (unless I go more than a couple back, but I'm not inclined to replay that much of the same game).
Assyria
I'm not sure if my poor experience with Assyria is a consequence of changes to warmongering rather than the civ, but I've been unsuccessful with them and, moreover, unsuccessful in a way that doesn't lead to an interesting challenge. Few of the changes in G&K and none in BNW strongly favour warmongering, so playing a warmonger feels a lot like playing vanilla - which, compared with the game with both expansions, comes up short.
Venice
I share the OP's experience. I raced ahead so fast in an Emperor game that I just got bored and left it by around 1200 AD, with leads both in score and in most demographics (and rapidly catching up in the remaining demographics).
I'll have to look up that advice. I rushed Currency in my last game (Morocco, Immortal), the first where I'd got a desert start with the civ, deviating only to take Writing, and Petra was completed a tech before I reached Currency, let alone started building it.
I have to say my longest, and most enjoyable, BNW game was with Siam, my pre-BNW favourite.