If you check the XML files...search in this path ....Program Files (x86)\Steam\steamapps\common ....plus a few more directories. The files are called CIV5Features and there are three different files...
If you look around in these files you will find the occurrence rate for all the natural wonders.
FoY is the rarest... 1 chance in 100 in a totally random map that it will appear somewhere. [...though I'm not sure how "random" any particular map is.] As rare as it is, it also has to appear near enough to your spawn location to be meaningful in the earlier part of the game when it gives you quite a kick towards Golden Ages and such.
I certainly don't turn my nose up at it if I find it early, but, playing as Spain, I would much rather find KSM ...occurrence rate 4, or LV occurrence rate 10..... or Kilimanjaro or Uluru, both at 10/100.... Then, of course, being the first to find Eldorado...2/100... as Spain is meaningful mainly for the 1000G it gives you.