The difference in price for a Disney adult (10+ years old) to get a 4 day PH versus a 5 day PH is $20!!! Now if you also get G+ each day, you have to also add that for the extra day. BUT, for me, $20 is an easy option to have a more relaxed, 5 day option rather than a 4 day option. I agree with you 100% that my favorite type of DLR vacation is the one where we fly into SNA, go straight to our resort (for us these days, it‘s GCH, but we have older teens so we can now all go to sleep at the same time, so we no longer need a suite), do our Disney days, and then go back to SNA and fly home. A very encapsulated vacation. We come and do separate beach vacations or see LA. I think the focused DLR vacation can be much more relaxed and enjoyable, especially for your younger child.
As for the hotel, the PARKS are really what is going to WOW your younger child. The parks and everything there will overwhelm her in a great way. The hotel will honestly be a place that she collapses into bed. So for me, if I wanted to save some money somewhere, I would do that at the hotel, and I would spend on the park days, G+ to relieve us of waiting in terrible lines, and the special things like character dining, etc.
As for your question about the VIP tour, as another poster said, sharing a VIP devalues it significantly to me. We have done many VIP tours, but we will only do it when we can afford it for just our family. The benefit of a VIP is doing whatever you want (if your kid wants to ride Dumbo x 10, go for it!). If you are sharing the tour, you are spending an awful lot of money to make compromises (unless the other family and you are very, very aligned in your priorities). I would absolutely do the 5 days, at a relaxed pace. When/if you can afford yourI am own VIP in the future, it is absolutely wonderful, but I would wait until your younger child is older and can get the most out of that type of very high paced day.