On this point: I am really enjoying the game I'm playing, to the point where I wonder if the vanilla effect of the extra movement might be better than the extra experience.
In my view, the best UAs are the ones that really encourage you to play that faction differently - not just in which units you build (which are affected by your UUs) but in how your empire works. To me, the extra naval movement really does that nicely, because it encourages you to have a farflung coastal empire. The game I'm playing on a Continents Plus map, I started on a mega-continent with 5 players, but I found it far more productive to hug the coast and expand to islands than to trek inland. The extra movement makes it feasible for me to police this territory, and really helps with the tyranny of distance that otherwise makes far-flung empires infeasible.
This has a great flavor effect; I really feel like I'm able to build a great intercontinental commercial and colonial empire, kept in place by the power of my mighty fleet.
The extra movement would be particularly helpful in the early game - the one thing limiting this strat is that it still takes forever to get settlers, workers and land units around anywhere in the early game. So that's when the +2 movement for embarked units would help even further. But this kind of strat wouldn't really be possible without the +2 moves on naval units - 3 move ships in the early game just aren't fast enough to manage to work with cities that are a long way apart.
So I wonder if it is worth reverting to the vanilla UA. That kind of mobility is more useful and is more interestingly different than just having naval units that are tougher in a fight.