Yes -- I usually spend about $0.35 a year at CET properties, but still get full Diamond perks with the Founders Card benefit. So considering how CET slots pay back, it's a real savings!

I stayed at the Nobu Hotel at Caesars Palace last fall using the FC discount, just to check out the rooms (with the discount, it was less than $150 the night I went). They waived the resort fee, gave me a discount at the Nobu restaurant, and left a monster amenity gift box full of snacks for me. I also like being able to go to the CET Diamond lounges for a glass of Champagne when I need a change of scene and don't feel like dumping more $ in the slots. And I get a line pass for buffets, etc., and free show tix every month, though I still haven't bothered to go to one.

I've also used Founders Card discounts to stay at Mandarin Oriental and Cosmo when I wanted a fancy hotel experience but didn't want to deal with chasing comps. I swear it saved me money -- those comps are expensive. Anyway, like I said, PM me if you're thinking of applying anyway, and I'll give you a FC invite code.

EDIT: My FC account for new member invites says it's "an annual rate of $395 (vs. our standard rate of $795)." I definitely wouldn't pay that standard rate! @sassycat, does your SIL have a lower rate she can share?