I just did my first, and maybe only for quite a while, Private VIP tour at the beginning of this month. We had 9 people in our group, and I thought it was more than worth it. By no means do I even remotely consider us wealthy; this clearly a splurge for us. I had originally planned to do one of the specific, not-so-spontaneous, tours; but with 9 people, and for a little bit more, the private VIP tour allowed us to have ultimate flexibility.
While I have heard people do multiple days, with multiple guides at times, we had our guide for 8 hours for only one day, in the middle of our 7 day trip. I was worried that we wouldn't get much done, but we were able to hit all 4 parks. The convenience of having a private vehicle driving us between the parks, and parking backstage very close to attractions, definitely helped. Not having to deal with buses, security and walking in the humidity was a luxury.
We were provided with light snacks and water twice during the experience. If you do decide to partake in getting food with your guide, they get Disney to pay for their meals (basically getting paid to eat churros should be a life goal).
We're originally from California and prioritized attractions that were unique to Walt Disney World, or drastically different from their California counterparts. Our cast member had a fun personality that made her feel like she was a member of our family. My group was made up of adult cousins and it never felt awkward having a stranger lead us around as we quickly warmed up to our guide. Our guide sprinkled in fun tidbits of information here and there about attractions, the resort, and her career at Disney. It was engaging, and never seemed "formal". Bonds were made that day.
The only relatively long waits we had, despite having Fastpass access, were for Buzz Lightyear at the end of the day (we originally had no intention to do it, but had time), and Alien Swirling Saucers (there was only one side running). Even then, being engaged by our guide in those queues made us forget about the wait.
If you want an idea of what we did, here's what we accomplished in 8 hours (we went at a steady pace when we did walk, never felt rushed... seemed like we were walking a bit slower than other guests around us):
-We were picked up at Jambo House at noon, after a filling breakfast at Boma...a great way to start off the day so you don't waste time (and money) eating at a table service restaurant with your guide. This allowed us to focus on attractions.
ANIMAL KINGDOM
-Na'vi River Journey
-Flight of Passage
-Expedition Everest
EPCOT
-Test Track
-Frozen Ever After
HOLLYWOOD STUDIOS
-Slinky Dog Dash
-Alien Swirling Saucers
-Tower of Terror
-Rock 'n' Roller Coaster
-Churro Break
-Apparent almost run in with a celebrity backstage.
MAGIC KINGDOM
-Thunder Mountain
-Splash Mountain
-Seven Dwarves Mine Train
-Space Mountain
-Buzz Lightyear Astro Blasters
-Snack Break at Auntie Gravity's in Tomorrowland
-Reserved viewing of Happily Ever After
-Guide understandably left us for 10 minutes to practically save a life by attending to a guest having a medical emergency shortly after the fireworks. SHE WAS AMAZING!
-Had a drive back to our resort, Bay Lake Tower.
The cost was $4000. Some of the more non-customizable tours range about $250 to $300. With the attractions we went on, we would have had to do a combination of multiple tours to get the same done, and still miss out on a few. I felt it worth was worth it overall, of course with our party of 9. Perhaps with a smaller party of 2-4 it may be even more a splurge. You may have different priorities, but the flexibility allows for it, and you may have a different sense of value. A lot can be done if you focus on Fastpass+ attractions. Non-Fastpass+ attractions may slow you down. Like others say, your mileage may vary.