FWIW, on my recent trip, I didn't mount my new ND8 filter even once, and used my circular polarizer less than I thought I might have before I left. Maybe because I was switching lenses so much, I didn't feel like switching filters, too. But I did wear my filter wallet on my belt every day so they were there waiting for me.

I also don't have a CP for the lens I probably used the most (31mm F1.8) and my second-most-common was my fisheye, which you can't put a polarizer on. I could have used one for my macro lens but my CP in that filter size is a cheapie and I didn't want to chance degrading my image. So basically, I mainly used it on my 50-135mm, and once or twice on my 28-75mm which I didn't use often. I do think it did help, when I did use it. FWIW, it's a Hoya HMC, which isn't too cheap but not to expensive, either - bought from Spotlight Camera on eBay, I've bought from them twice and had very good results both times.
I don't think you'll find much use for ND filters at Disney parks. If things are so bright that you'll need one, then chances are it's midday and very crowded, and you're trying to get a slow shutter speed so you'll probably want to use a tripod or at least monopod, which will be even more of a pain during the day than in the evening. You need to be really after the photo. Even with all the gear I have carried my past few trips, there are shots that I think would be good that I just can't be bothered to go through the effort of taking - and that's saying something.
I personally don't think a split will be very useful either, as you'll rarely see a clear, open horizon - most of the time, you're looking at various buildings and structures, and those'll get darkened along with the sky.
Again, just my opinions for Disney park trips only. Not applicable for non-Disney-park situations.