I decided during the 50th anniversary of DL that it would be cool to visit all Disney parks during the celebration. I got about half way through. I frequent DL, so that was an easy one. I was able to get a week in at WDW and a few days in Tokyo. All I had left was Paris, then Hong Kong opened, so that left me with 2 still to do. Well, my friend who usually travels with me decided she wasn't able to take any trips this year. (We were planning on Paris in the spring). So I plan and take an non-Disney trip, once I get back she tells me she rethought about it and could probably go after all. Well, um, thanks, but I've already spent my money and used my vacation time.
But...I'll be bringing the Magic home from the Mediterranean next year. So before we catch the boat in Spain, we're spending a few days in Paris.
As for when to go, DL and WDW have the same patterns. Stay away from holidays and summer. In Tokyo, there's not really a slow season, at least not that I was able to figure out. I went on a Monday and Tuesday in November and it was pretty crowded, but not unmanageable. Then again Japan is just pretty crowded always. For Paris, I've heard Nov and Dec are good and August is bad, it's just too hot. So guess when I'm going? August! Couldn't help it, that's when the cruise is.