Sorry I'm late to the discussion! We live in London and first took our wee one to DLP when he was 2.5 (I would never have gone during the "nappy years", mostly because my kid had a paralyzing fear of public conveniences). This (age 2.5) was great. It was May - warm but not hot - and we stayed on property at Newport Bay Club so we could walk/push the stroller to the parks. We would go out first thing (easy with most toddlers as they are up EARLY), walk back to the room, take a nap and then go back out in the late afternoon.
I have some wonderful pictures of his BIG EYES on rides as he just took in everything around him. We also have a couple of cute character photos but these are much harder to get at DLP (in the parks) because it is a free-for-all to get to the characters (correct me if that has changed!). A character photo with a tiny one is ADORABLE!
We went back to DLP 2 years later - brought the stroller but never used it. And while we loved the big eyes of our 2-year-old on our previous visit, taking a walker was SO MUCH BETTER. The only thing I missed about the stroller was its second function as a jacket/poncho/drinks holder. For what it's worth, my kid has always been a good little tromper (when you live in London you want your kid out of the buggy and walking ASAP as buses and the tube are a BEAR with a pushchair) and DLP is pretty small.
WDW, on the other hand, is both huge and HOT (like walking around in somebody's mouth hot). My hubby and I decided we would wait until our guy was six to make the trip to Florida. In my opinion (and it's just that!), this was THE PERFECT AGE. He was young enough for real wonder (I stopped photographing the Electrical Parade to take pictures of him WATCHING the parade) but old enough to walk, everywhere. The other thing that made a huge difference was at six...he could read, really read. Kids who can read can be so much more involved in the trip (can you tell I am a bookworm?). Our wee man LOVED reading the signs, maps (!), menus and...autographs! He read them (and still does) over and over and over and over...
Just my two pence worth - hope it helps (a tiny bit?)