I'll answer what I can
Hotel accomodations:
- SPG Platinum, will try to get Loews Plat
- Total of 4 adults in one room. Price is a concern but not that much if we can get anything with more space (I saw the difference between the universal resorts is less than $50/night). Having a suite would be excelent. Two double beds at least.
It's going to be tight in any room, including the Dolphin.
Travel Plan-
Arriving DEC/30 to WDW Dolphin, hopefully spending New Year's eve in MK. Is it worth? Any other recommendation?
This is the SINGLE busiest day in any of the parks. The MK will most likely close sometime that morning. If you can get in, you will be with around 50,000 of your closest friends
You have a better shot at Epcot and if you're at the Swan or Dolphin you can easily walk in and out of the park.
I was there a few years ago on NYE, and quite honestly, did not dare to enter a park that day. We had a nice dinner and watched the fireworks, which were exploding 360 degrees around us, from our room. Traffic was a nightmare, the entire holiday weekend. I did it once and doubt I'll do it again.
Keep in mind that while at a Disney hotel, of which the Dolphin is considered, they guarantee you entry into
A park on NYE, not necessarily the one you want to be in.
We are thinking to switch from the WDW Dolphin to an Universal property on JAN/7, giving us 2 nights, 3 days at Universal. We would have stayed at the Dolphin while doing Universal but the Express benefit is a plus as we want to do Islands of Adventure while the kid does Universal Studios with grandpa and grandma.
Given what you'd like to do, plus the benefits of front of the line access, I would go for it. Keep in mind that after the holiday crowds leave the entire area will be nearly empty. No, I"m not kidding. The week after New Years is the slowest of the year. Moving hotels may not be necessary. Or, you may want to do it for 1 night and use the access for 2 days - It's good from check in to end of check out day.
Does weather play a role here?
It could. When we were there I didn't pack shorts because it normally doesn't go much over the mid 70s. We hit the mid 80s and I went home with a tan
I had to buy shorts.
Last year, I nearly froze MLK weekend. It went down to 34 one night. Luckily I brought gloves from home.
Would you go to wet 'n wild? Or shall I leave this for july?
I wouldn't go at all. If you want to hit a water park, the 2 Disney Water Parks are nicer than Wet & Wild. But they're usually closed in Jan because the weather is so variable.
Wait until July when it's 95 with 90% humidity