Send Dementor a U2U. He used to have one fitted when he had an ST.
I assume that you're talking about the previous ST, before the facelift, because the new bikes have a huge fairing and adjustable bars as standard (I don't even think there is a comfort kit for one of these).
The comfort kit for the older bikes consists of a different headlight fairing, a taller screen and some bar risers that lift the bars up about an inch (maybe a bit less). I reckon it depends on how tall you are and what you want the bike for. If you're 6ft 10inches tall and ride long distances all the while, or if you have old injuries and creaky bones then I can see the point. Otherwise the standard ST is comfy enough for most and that comfort kit is one ugly mother.