I agree with those who say that the decision must be weighed against future travel plans. As part of that, the $1,100 cost must be netted back against the benefits because the entire amount is not the true cost. Miles are, in effect, a rebate in the form of future travel credit.

Assuming you have the $1,100 -- and I happen to see that as a lot -- then you can subtract the value of the 20,000 miles. In my own case, I use 1.5 cents/mile, so it's $300. You should also factor in the lost opportunity to gain miles that you will be saying goodbye to by not making silver, so if you would have flown 25,000 miles during the coming year and it's a 50% bonus to be silver, then it's another 12,500 miles (or $197.50 at 1.5 cents/mile).

Alright, we have netted the $1,100 down to $602.50 and you now need to make a SUBJECTIVE judgement on the value of elite status, as well as any economic value that the status might have to you.

...Of course, the $1,100 is paid after taxes while mileage and other elite benefits are outside of taxes, so crank those factors in and you end up with about.... hmmmm.... about an $1,100 difference?