I'm currently pondering this and imo the best thing to do is limit Cotton, Spices, Tea, Coffee (maybe also Tobacco) to say, 4-5 occurences globally so that it's difficult to get all of them and maybe have some of them only give +1 happiness with the right building. Since currently Spices apparently also represent Tobacco, its spread can be toned down a bit (we have to think of something for the Dutch UHV then).
I think all Plantation Luxuries (except Silk) should be affected, namely Dye/Incense. I have a feeling that currently Incense represents most Tea/Coffee, and there are a bit to many Dyes on the map.
The Dutch UHV could simply be changed to "Get X Plantation resources" instead. About Dutch games in general,
(A) Currently the UHVs plus the 1500 start time means that Dutch games are all really short, even on Marathon.
(B) Dutch AI's culture is horrible, which I find lamentable since I'm a big fan of Dutch Golden Age painting.
(C) Even the new UP isn't that powerful, again due to the uber late start. I cannot get as much yield out of Trading Company as the Dutch compared to what I can with England or Portugal.
(D) Your UHVs should be won before you get Steam Power, i.e. before you build the legendary Dikes, making them useless.
(E) For the current UHVs, a valid strategy is to not found Amsterdam at all, and instead found your capital in the Americas (New York, even, since your UHVs will finish before the American spawn). Then you don't have to worry about pleasing the Germans and the French, and simply focus on commerce and UHV.
I suggest a few Dutch buffs:
(1) Trading Company spreads to Amsterdam;
(2) More starting Culture techs (Aesthetics, Drama, Literature, Music);
(3) Flood Plains near Amsterdam, or additional Food resources;
(4) Lower tech requirements for Dike, e.g. Replaceable Parts (The Dutch starts with Engineering but not Printing Press).
I intend to make some changes to religions in 1.9, mainly that non-state religions cause extra unhappiness that can be offset by building temples, so they give you a net zero happiness gain (basically the SoI model). Syncretic combos like Hinduism + Buddhism and Confucianism + Taoism might be excepted. Free Religion would then only offset these penalties instead of being a happiness wonder.
Even though I'm a Free Religion addict I must say these are plausible.
But additionally I think Confucianism/Taosim should be more compatible with other religions, or at least Buddhism if you're going for historical accuracy:
http://en.wikipedia.org/wiki/Religion_in_China
http://en.wikipedia.org/wiki/Three_teachings
http://en.wikipedia.org/wiki/Neo-Confucianism