My Golf had the Life Shine done when I brought it and that was 300-400£, and it has made NO real difference to the resale value maybe a 50/100£ but only because the car looks well cared for.
So i am not going to bother. My car previous to the Golf looked as good if better, and I had that detailed first and then I kept up the shine myself.
Used to spray off as much of the dirt, then using 2 buckets, 1 x wash and 1 x rinse bucket, would have a warm soapy wash and clean water rinse for the washmit, then spray off.
I then dry using large microfibre towels. Then using Sonax premium Paint cleaner, then apply Sonax Premium Carnauba wax.
used AutoGlym Alloy wheel cleaner, and tyre and rubber protector.
Interior, Autogym interior shampoo. But I am changing over to Chemical Guys cleaner and protector for the Alcantara seats.
I will give the Golf a good wax and interior clean before it goes in May. Will use the Autoglym wet wax, which is really quick and easy.
and works well with the life shine.
So You don't need to spend out on these dealer ones, I would side with Dolphin on this one. Get it detailed and then keep up the shine yourself, or do your own detailing. Loads of instructional videos on the web.