I'll agree with everything else you said, but... wobble board split squats? In years past, I've trained on unstable surfaces and noticed zero carryover to skiing. Wobble boards and bosu balls improve your balance on... wobble boards and bosu balls. Likewise, I spent alot of time walking a slack line thinking it would improve my balance for skiing and climbing. The only thing that improved was my ability to walk a slack line.
I have to say that balance is one of the most sport specific skills around. Example: I've been skiing since I was five, and racing since I was twelve. I'm pretty competitive in both alpine and telemark racing. I daresay that my balance is pretty well developed when it comes to both alpine and tele, but whenever I get on my nordic skate skis I flail around often fall. Keep in mind that the jump between telemark skis and nordic skate skis is very small compared to the jump between alpine skis and a wobble board.
In a sport like skiing, you're better of training muscles rather than movement, since it's almost impossible to mimic the movements of skiing on anything but a ski run. Wobble boards decrease the load you're able to use, and therefore limit how much you can train your muscles, so I'd consider them detrimental to your training.
Unstable surfaces have their place - and that place is physical therapy and rehabilitation, not training for skiing.