It's okay if you want to spam out settlers for a major land grab, just make sure you don't go over your current government's OCN, or you might end up in a situation where you lose almost half your empire to the AI because those cities are only bringing in 1 SPT and maybe 3 commerce with a FP and courthouses in every city. If a civ is Ag/Comm, or Ag/Rel, I might go for it, otherwise IMO it aint all that great. True, I've seen Ag AI civs (dutch, celt, etc) explode in the Ancient and middle ages, but with a Sci or Rel civ you can beat 'em in the tech/culture races and use your superior units to prune some of those unproductive (due to corruption), deadwood cities from their empire.
Another thing I don't like is that almost no city improvements are Ag, while there are a ton of industrial/religious/scientific/commercial/military improvements, although I do like half-cost Recycling plants.
The main thing I like about Ag civs is that settling the Sahara (what I like to refer to ~30+ tile deserts that tend to crop up right outside my territory) is actually a viable option as long as fresh water is available somewhere (I once had to irrigate 15 tiles just to be able to irrigate in a desert city's radius, but it was well worth it).
