Everyone is different, but since I now find myself within driving distance (9 hours) of WDW, I took a gamble on some short trips with my young son. When you can drive, there is probably less hassle than planning a huge trip to make the flight cost worth it.
I had my doubts about taking a toddler, (what can he go on, what about naps, what about the weather, what about those long days?) but we had a group of friends (with slightly older kids) going to WDW in the fall of 2014 and renting a giant condo and we wanted to join them. So we took my son when he was 2 and we loved it so much we went again on right before his 3rd birthday with his cousins. Both trips were only two park days each so as to not "push" it. It was affordable, but still magical (even though so short).
I was encouraged to go BECAUSE the price is right (free under 3). To me there is less sense of "waste" if you aren't paying for the child. Plus if you hit the buffet meals, they get a decent meal with a wide variety of choices (for free).
I mean . .we made some sacrifices of course. This wasn't a "big" trip in any sense. My wife and I didn't hit the big rides, we got Fast Passes for inefficient things just to skip ANY line possible, we did character meals to avoid standing in line to see characters (and that helped as well since the characters come to you). It was about letting my son experience the Magic (and we knew we'd be back).
Heck .. these trips went so well, we went back again this March with an even YOUNGER child - when my daughter was only 5 months old. This trip was another friend trip, so it was mainly for my son (4 yo at the time) to go to the parks with his best friend and their family. We pushed it this time .. two park days and a day at LEGOLAND, but even with a 5 mo, it was a great trip. Again .. sacrifices had to be made (rides skipped by one adult or the other, leaving before the night shows, skipping a park (AK), etc.).
All three trips were such great fun and relative ease that we'll be going back again (probably in a year) once my daughter is 2 (my son will be 6), so she can have a similar experience and actually enjoy the rides and characters. Though this time, we'll probably go on a longer trip (3 park days) since we know how to handle it and my son will be older and want to do more.
Basically I would encourage ANY family to take a child sometime before 3 to take advantage of the price of admission being free. The cost savings is tremendous. Do what I did and go ON your child's birthday so they are as old as possible --as long as you check in before the child turn's 3 .. they are considered "2" for the entire trip (and makes it a fun celebration).
