I say go for it! We took dd when she was 21 months last year and will be taking ds who will turn 7 months while we are there next month. No, he won't remember it, but like the pp said, we will and will make some great memories. Yes, it will be a hassle with 2 car seats, 2 strollers, and all the stuff that you have to have with a baby, but we can't wait.
When we took dd for the first time, we had a whole different trip than we had every year prior to that. We went to character meals for the first time, rode rides we had never been on before, spent a lot less time in the parks (which was just fine), missed some things we used to do, but all in all, I wouldn't have changed a thing.
Not everyone will want to take an infant, but if you do, you will still have a great time in WDW. Best wishes on your new addition!!!!