They do have some nice resorts to exchange to, but there isn't a good way to see what they have in inventory even with a membership. You can see what they have in short-term/last call availability looking at their "
Resort Escapes" page. They have a fairly close relationship with Vidanta and therefore get access to bulk inventory in the Grand Luxxe resorts at the suite level, but typically not in the higher tiers. They also have an arrangement that results in lower resort fees there ($75/week rather than $950 for a 2 BR Grand Luxxe in Nuevo Vallarta). Other resorts in Mexico you can get through them are Sheraton Buganvilias, the Pueblo Bonito resorts, and some others.
IMHO, using a high cost TS to trade in SFX is probably not the best use of your ownership. Using the Diamond level membership with SFX, you get a one room size upgrade and some other benefits, so it's generally not worth depositing a 2 BR week with them. While it would be great if more people deposited good weeks like OP's ownership, the vast majority of the inventory SFX has available is bulk deposits from the Mexican resorts and you can trade just about anything to get them. I, and many others, use less expensive stays to trade with in SFX. Typically I use a studio or 1 BR from Wyndham when I have excess points there and sometimes get those upgraded and get credit for the larger room size with SFX as well.
If you're looking for a more even exchange, you might consider looking into ThirdHome. They have more high-end timeshares as well as a number of vacation homes. There's one person that has established an account with them for
Grand Waikikian and it looks like it gets fairly decent trading value with them. PM me if you're interested in further details on them and I will share my POC's contact information.