Sounds like you know the parks well then? I would give serious thought to the tour, especially with the lack of great nighttime shows where you used to get VIP seating.
We just took a tour at WDW this past Sunday. We tipped $700 for the 8 of us. It was about 18%. The way I see it, it is a service just like any other. They don't make a high hourly rate and have to put up with a lot of BS in most instances (we saw several snarky tour groups during our time). It is worth it to me.You tip your VIP Tour Plaid $800? I can tell you we don't come anywhere near that. There are three of us. We tip them, but definitely not 20%. The number of people in the tour is a factor for the amount of the tip as far as I'm concerned. If there are 10 people, then likely a tip could be more. It would have to be a stellar Plaid who goes above and beyond. In fact, some guides have been very lacklustre to say the least, compared to others. A tip should never be "expected" at any rate.