Well, main reason I want to do the real dash is just for the ergonomics and clean look that everything would have.
I don't think it would be akward to be LHD on the screen and RHD in the cockpit or vice versa really. If you have the FOV set up correctly, you will barely notice anyways. My center screen will be centered over the wheel, so I don't think it will be a problem. For open wheelers, again, the FOV makes this not much of an issue. When I've got 3 42" screens about 26" from my face, I don't think I'm going to be paying too much attention to the cockpit anyways, but the ergonomics of button/switch/shifter placement without having to fabricate anything is a great solution in my mind.
Another thing, I'm not trying to replicate any particular car, to be honest I don't even really like Supras or RX-7's that much, I'm more of a Euro car guy. What I did though is look at what I have available to me fairly commonly in junkyards, and browsed around looking at the interiors, I looked at everything from Nissan Bluebirds to Toyota Altezzas to Nissan Skylines, the two interiors to me that seemed they would function best in a sim racing environment were the Supra and RX-7.
Another benefit is then having some space underneath everything to work with for running (hiding) wires and even building a place for my computer to go (under the center console I'm thinking). So I could have everything kept internal in the cockpit for a much cleaner overall look.
Oh and I do have a single Aura Bass Shaker mounted to the seat rail, forgot to mention that one in the original post. One is enough for me, but maybe eventually I'll add more.
Take a look at this thread, posts 289 and 290 specifically. Here's an example of it:
http://www.avforums.com/forums/11266718-post289.html
Due to my cockpit design, my wheel would be centered on the center screen though, so it wouldn't have that awkward offset.
I'm going to do it, not for the immersion factor and not to replicate and certain car, but for the ergonomics and the obvious "bling."