I would suggest asking this question on the WDW Strategy board.
But what I have read about VIP tours that it can be quite tiring because you do not (/hardly) wait in line. You can do more and the guides take you at a high speed around the park(s) to do as much as possible. If your child needs a break or if the best decision is to leave the park entirely for the rest of the day, there is a fee involved to cancel the tour within 48 hours. I assume that if you cut your tour short, you lose the full amount.
I would suggest to better spend the money of the VIP tour on more days and take things slower. WDW is a wonderful magical place, but also with a lot of stimuli, not every child handles this well. With more days you can visit the parks in the morning, have a break in the afternoon, go back to the hotel, time out, relax, have a swim. And then go back to the parks in the evening for more park time. With less days you will try to do as much as possible get your time/money's worth.
We have been to WDW before and will do 4 full park days before the next cruise, so we can visit each park. We already know it's going to be too short, we have to make choices on what we see.