I've been to Porta Vallarta, Mexico during the spring break time frame while I was in the Navy. (one of the few good times I actually had in that f***ing hell hole)
I would probably say it has a similar nightlife atmosphere as Cancun. This is my take:
Yes there are lots of western woman there who are just there to party every night in clubs and get wasted and perhaps surrender themselves to some lucky bloke every night or just have a vacation fling.
Most western women are much looser on vacation as they feel they don't have to worry about their self-image as much as they are far away from their normal social circle, so they tend to go wild. However, guys who are less than a 7 on the looks department will still have trouble hooking up as there are just as many single western girls there as there are western guys, its just that there is more of an even distribution. Unlike in the states or other western countries where it is more of a sausage fest and most guys have to compete with each other to land the hottest girls.
I personally would not go to any vacation destination that is a famous western tourist destination looking to bang chicks, as your odds aren't going to be much better there than back in your own country unless you are a stud muffin and aren't afraid to go up to chicks all the time in bars and clubs like you would in a western country. The rules don't change much, its just a little easier to get laid there than in the states as the girls are usually waster and alcohol makes women do strange things...
There are the typical Mexican whore houses and massage parlors but they are not much different than going to Tijuana or something like that. Maybe just a little safer. Your not going to have a GF experience or anything. It's juts going to be strictly paying for timed sex and if you get your rocks off doing that with a potentially hot Mexican chick, than good for you.
If you want to go to a Latin country and you are a male wanting more of a sexual vacation I would just go to Columbia or Brazil, f**k Mexico. I'll go to Mexico for actual sight seeing the pyramids and all that. For the naughty nite life I'll go to the known hot spots like Columbia or Brazil!
Personally I still think Thailand is the ultimate single guy paradise for naughty nite life! Philippines is pretty good too. It's relatively cheap and the girls will treat you well as long as you treat them well for the most part and a majority will give you the girl friend experience. This is actually quite rare in many countries. Most guys wouldn't really know what I am talking about unless they have been to either country.
One last thing, if you want to take your chances to bang a decent looking western chick I would go to Bali not the Caribbean or Mexico. Bali is known as the top Australian vacation spot and I've been there twice. I can vouch it is a good place to pick up Aussie chicks if you can be patient and talk up a few each night at the bars. I never actually scored with any as the few nights I could have, I got super wasted on Jam Jars (this concoction of hard liqueurs that taste like tropical juices, so good, but gets you so f***ed up!) and embarrassed myself. Also another night this one chick was giving me the eye as I was in the hotel pool at night drinking, but I had to take a super huge piss and didn't know where to go as everything was closed around the pool. It was not my hotel so couldn't just walk to my room and at the time. I thought pissing in the corner or in the pool in front of everyone wouldn't look too great. So I took off back to my room and then wasn't allowed back into the other hotel as before I came in with a bunch of Aussies as an invite. This was in my younger years when I didn't know shit about women. I think if I went back there today I would definitely score with an Aussie chick.
Gotta watch out for those Jam Jars! They will bite you in the ass!