The first time I stayed at the Polynesian, back in '03, we were in Tokelau, and they were redoing Hawaii. You couldn't really sit out on the balcony due to the construction workers there all day. You had to keep the drapes pulled....it was less than wonderful. But, nothing was offered. We had gotten such a great rate that we just lived with it.
Then, last year, my friend booked us into VWL in early Sept....yes, the time when the main pool was being closed! Guests were told they could swim in the DVC pool..which is much, much smaller than the main pool. My friend was refunded a few points back to her DVC account but nothing other than that. I believe some cash guests were given passes to BB, or credits to their room accounts. No such luck for us.
If you find that there is going to be construction or such during your stay, it's a good idea to call Disney and see what can be done. They may be able to get you into another resort, if that's what you want. But they seldom make refunds.