I've been to the Guadelupe Valley, where most of the wines are being produced. Some are good, some not so good.
L. A. Cetto is a big time operation.. think Mondavi, with all the modern equipment you can imagine. The wines are just fine for what they are, and every now and then, they can be impressive (I'm thinking of a Petite Sirah they made, for example).
If you continue past L.A. Cetto on the little dirt road, there is a little mom and pop operation, which is now just a mom operation, called Doña Lupe's that is worth a visit (here's her website
http://www.bajawine.info/wineries/la-casa-de-dona-lupe.htm and
http://casadonalupe.com/Homemade_Wine.html ). I've spent hours there with Doña Lupe, who also sells nuts, honey, another goodies. She has gotten a wee bit commercial over the years, but, hey, she's still a hoot.
Monte Xanic is, I think, a very high quality producer, especially of the Cab and Cab blend. Definitely worth seeking out and visiting.
There are lots of other small places to try.. and all have tasting rooms of sorts (with
L.A. Cetto's being Napa-boutique in style).
There are some very good, top shelf restaurants in the valley too.
The only problem is getting wine out of Mexico back into the US. You can only cross the border with, I think, about 3 liters per vehicle.. which is a bit of a joke. However, it does seem that some of the wineries do ship (see links below). Here are a couple of websites to check out.
http://www.discoverbajacalifornia.com/wine_country/wineries.htmhttp://www.mexicomatters.net/travelinginmexico/07_valledeguadalupe_ensenadamexicowinecountry.php