Yeah, I pretty much agree as well. I've heard some interesting things, like since stainless steel is more rigid, it'll be more true to the force curves of the switches, but it goes beyond that, of course. Force curves don't really tell you much about the impact you're putting on your joints when you're bottoming out on a switch. For tactile -ALPS- switches, using a steel plate in a rigid case with something like Alps SKCM Brown or SKCM Amber is killer on your joints, even SKCM Orange got to me on my bent case Infinity and caused mild RSI.
One of the most pleasant typing experiences I've had has been with my NCR Alps build with SKCL Browns, using an original OEM Alps plate in a G8X-3000 case. It has just enough flex, and the case makes it softer too, so it just ends up being very pleasant.
On an aluminum custom, if you want a more rounded feel, I'd go with aluminum plates. Linears do feel good in rigid cases though, but I think they'd feel good with aluminum too.
I also agree that top-mounted cases are much more forgiving on one's fingers. Tray cases are much more harsh in comparison. There is more inherent flex in the plate on top-mounted designs, but this isn't necessarily a bad thing. Too much rigidity is bad and so is too much flex.