Aaron brought up many interesting topics in his "Case in Point."
I've always looked at the agencies (including correspondence agencies) as a convenience for those of us who can't afford to or choose not to live in Latin America.
I've always suspected I could have better luck finding the right woman if I lived in Cali for a time, maybe 6 mos. to a year instead. But for various reasons, I chose to make the regular short trips of 10-20 days. So far, I'm still single, but that has more to do with me & my own trial-and-error process. Fact is, I've met many wonderful ladies in the agencies, definite marriage material.
I've also made a number of Latina friends both here & abroad. Interestingly, almost none have ever sought to introduce me to eligible ladies. Fewer than my American friends (men & women) and far fewer than the Filipina ladies I used to work with. Those gals are veritable matchmaking machines. Even tried repeatedly to hook up a gay friend of mine once (chuckle).
My theory on the lack of matchmaking Latinas has to do with their famous jealousy & possessiveness. Just don't want to share their amigo gringo with another female, it would seem.
As far as the socioeconomic issue, I've noticed a universal law at work: The more we have, the more we want. The better educated, upper-middle-class women I've known (Latina as well as gringa) have more options, so they have higher standards. They generally want guys who are younger, better-looking, and with a higher standard of living.
I've had several sometimes painful experiences with such Latinas; they can be quite demanding, though not nearly as much as gringas in their position. And while such "high quality" women don't often join the agencies, I suspect they're also harder to attract & keep.
Class-wise, our best results as spouse-seekers seem to lie with middle and lower middle class Latinas, women who want to leave their country and "get ahead." Thus, Colombia is the perfect place for so many of us.
Just a pile of generalizations & opinions, of course, based on my own experience. YMMV...