OP, we're going to DC for the first time this summer so I can't talk you any which way

.
Where are you going to be staying? Is there regular transport to & from SW? Because from SW there are shuttles to Aquatica and DC which won't cost you anything.
If free transport isn't an option you might want to look into renting a car. We did that for the first time last year when I discovered that it would be cheaper to rent a car that to pay for transport to & from the airport alone.
Of course if you're staying at a Disney resort & using magical express transport to the airport isn't an issue.
Then again, in the grand scheme of your vacation $ 1400.00 isn't a huge amount (OK, granted 1400 is usually my entire vacation budget

). DC is an all inclusive day so you won't have to worry about meals. The earlier you book DC the "less" the admission costs...you can always cancel 30 days out for a full refund if you really think it's going to be too much.
Now, a word of warning...DC is more than just the ticket cost. Carefully consider if you're going to want a cabana, photo package or any extras. Our cost all told for a family of three is pretty scary BUT I figured that if we were going to do DC we were going to do DC and I didn't want to have any regrets about it...cutting out something to save money then ending up wishing that I had done it.
So I'm not help...but I can get back to you after our trip and let you know if I thought it was worth it. You can call me Mrs Krabbs (ala SpongeBob) and I'll let you know if it was worth me money

.