I find that Carapils works well to increase body, without adding the residual sweetness you get from higher crystal/cara malts. I have found that mash temps don't really have as much effect on body as the grain bill.
I agree with your first sentence, but to the second I would counter that you just aren't mashing high enough. I haven't seen any appreciable difference in body even mashing as high as 156. It's not until I hit the 158-162 F range where I've seen an increase in body. I think that most of the malt we're using nowadays are so loaded with enzymes that even in the mid 150's they've done their job before the majority of them have denatured.
I mash barleywines at 148, session beers and anything seeing some Brett at 162, and everything else at 153. But I do think you have the right idea for the proper use of CaraPils.