I really think you have to go "all out" for the vouchers to pay off. I looked thru several lunch menus, and the best deal I found would be at Rainforest Cafe. You can get crabcakes ($7), and an expesive entree (like stuffed lobster, or king crab $30-40), dessert ($7) plus drink, tip and tax. All that would be about $60, all for one voucher you can buy for $30 - BUT who could possibly eat that much!?
Here's what we decided to do. DH and I are going to use one voucher and get "the works" PLUS maybe order a smaller (cheaper) entree and drink, and share the rest. That way we don't force ourselves to eat our money's worth, but we still have the advantage of ordering some of the expensive items (that sound really good).