Well, I just successfully modded my graphics and am very happy with the new look:
Most modpacks worked--the one I tried that didn't was Il Mafioso's Usability Pack, which just totally messed up the units and buildings in the city screen. I assume that since I saw no complaints on the thread, this problem is mac-specific.
Things that worked:
1) Thunderfall's less yellow. I like this best for most flat terrain and water (thanks Thunderfall!), but Sn00py's mod was better for a number of things (see below), so I mixed and matched.
2) Sn00py's Terrain mod--works fine. I love his forests, jungles, mountains, and rivers, so I used them. I dislike the rather oversaturated green of the grasslands and hills, the oceans are too blue (for me), and the plains and desert are still too yellow, so I used Thunderfall's for these (see above). I liked Sn00py's irrigation (it looks kind of artistically painted, like Van Gogh's countryside to me) better than Firaxis', but not as much as Zeb Fisher's irrigation (see below).
3) Zeb Fisher's Irrigation--This is really excellent. Grassland irrigation looks superb and crisp, kind of like neatly planted crops actually look when viewed from an airplane. Plains irrigation (which was actually Zeb's grass modified by someone else) looks great too. His desert irrigation (as adapted by the same 3rd party who did the plains) has too much gray for my taste, but I still preferred it to Firaxis'. Tundra irrigation is not addressed. The neatest thing about Zeb's irrigation is he's added little randomly-placed farm buildings on occasional plots of cultivated land. This terrain mod is so pretty, I've even decided to irrigate some land where my city could use more shields, just because I like the way it looks!
4) M_M_X's Barb camps, goody huts, and mines--I installed them and I found the mines slightly less ugly and obtrusive than the original. I haven't started a new game after the installation to check if the goody huts and barb camps worked yet, but the screenshots on the thread look great.
5) SkankyBurns' improved resource visibility--works great. Doesn't interfere with terrain too much and makes strategic and luxury resources really easy to spot.
6) Cassembler's skinny roads--works. I prefer them marginally to the original roads, since they don't deface the overall terrain look as much as do original roads (which are particularly ugly when all squares are roaded-up). However, they can be somewhat difficult to see, and I can imagine some people won't like this.
Overall, I was very impressed that A) these things actually work across platforms, and B) you can mix and match different people's mods to your taste, so long as you have some clue how the mods interact (and I'm no programmer, just fiddled one night to get it right).
Now if we can only get our hands on a mac port of the new 1.17 patch!