Aquinas,
First off, welcome to Flyertalk!
I did a search for you, using the words "Puerto Vallarta" and didn't come up with much useful information (other than a lot of posts telling people to use 'search'....hmmmm). Most of the posts I found with any info at all (mostly very limited) were from 2002 and prior.
It appears that FT isn't going to be too much help in this instance. If you have your heart set on the Marriott, I'd say go for it. I've heard good things about the resort (they do a sea turtle release program in Aug and Sept that sounds like fun) and it looks very pretty. I don't know much about Puerto Vallarta itself.
http://www.casamagnapuertovallarta.com/
This link may help you some.
If you have the option for the Westin, you might want to check the Starwood forum (search under Puerto Vallarta; PVR and other 3 letter airport codes don't get picked up well in searches). I'd also check the Travelocity trip advice area where hotels ar reviewed and see what current info you can find.
Sorry we couldn't be much more help. If you DO go, be sure and come back to FT and give us a hotel review! Have fun!