Let me point out that it's only September.

If you were going to have a big dinner next week anyway, and (as stated in recent messages) you're already Elite in DL iDine for this year (but not for next), then that makes sense.

But even if you are already DL iDine Elite this year but not for next, going out of your way to have a big dinner does not necessarily make sense compared to requalifying by just dining 12 times (no miminum) this year. (And since it's only September, there's lots of time to get in 12 dines still!)

Miles are in general only worth it if you can earn them without spending way more money than you would have otherwise. iDine is an awful way of buying miles (10c a mile!) if you're not getting anywhere close to the same value out of the dine as you would have had you not been using iDine.