As far as the California is concerned, if you have a wonky table then Parkers Price Guide might come in useful.........but that's about it.
IMO, the only way to price accurately is to carry out a price survey of as many vehicles advertised both through the trade and privately. Make sure you look at as many sources as possible e.g Ebay, VW Commercial, Gumtree but best of all the Club "Calis for Sale" section. Note down vehicles of about the same age and with a with similar spec, condition and mileage to your vehicle. That should give you a good average ball park price to ask for your vehicle. Also watch how quickly these vehicles sell. If they go quickly then you might consider asking a little more for yours but if they are advertised for a long time then they might be over priced. Also, if you are selling a very late model T5 then you should also look at the prices of the early T6s as many buyers would probably prefer the face lifted version if the prices are about the same.
The time of year also has to be taken into account when pricing. You may get more in the spring than you would now in the autumn. However by then the car will be older and a new registration will be upon us so the value may have dropped. So whilst you can ask what you like but you may have more success at different times of year.
It really comes down to how quickly you need to sell it. If you aren't fussed if it doesn't sell but but would part with it for the right price then go for the very high end of the survey prices and see what happens.