Since your list is for "nice to have" items, it makes it a little tougher to place emphasis on one spot. But here's my opinion.
Again, these are just my thoughts and opinion.
DLB
- Camspray electric pressure washer
I think this is almost a must have tool for proper detailing (a pressure washer that is). They are great for engine detailing, washing mats, and of course the usual wheel arches and pre-rinse. When I am doing traditional washes, I always have a pressure washer right beside me for various tasks. - vx5000 steamer
As someone else mentioned, this has multiple uses, and can also be used in household cleaning, so... - highline paint meter
If you are planning on wet-sanding or doing much heavy correction, then this would move up the list. It would be a nice "compliment item" to have however for the discriminating hobbyist. - CR-spotless
It is a nice idea, and I wouldn't mind having one...but, there is a maintenance cost, and you can avoid water spots in other ways. - Flex light-weight rotary
Just a pure luxury item for you since you have a rotary already that can spin the largest pads. - carpet extactor
Makes volume work faster, but for a hobbyist - just don't see the need.
Again, these are just my thoughts and opinion.
DLB