If you do a lot of traveling, where all the major airlines/hotel chains/car rental companies/etc. take Diners Club, you might consider it. It transfers to AA with no annual limit. The $80 fee is more than made up (the first year) by the 12,000-mile new member bonus - 1,000 miles each month that you charge anything at all. (When you talk to them, note that they talk points, not miles. Two points equal one mile.) Reportedly they offer retention bonuses, smaller but still worth more than $80, to renew after that.

If you want DC, find a member to sponsor you. The sponsor gets a few thousand miles. You still get everything you would get by applying directly.