You have to remember that they are 4WD. So that means transfer case, front driveshaft, front axles etc. They also have 4 wheel steering and they are a 2+2 sedan. So there is a lot of stuff. I think pound for pound they are pretty fast!
My R32 weighs 3440 with driver and a 1/2 tank of fuel, so it's not that heavy.
I had a 90 300TT it weighed ~3450 LBs. Anyways the chasis has to be rigid enough to handle the power and outside of carbon fiber-they get heavy. Also, hightech accessories, i.e. Hicas, turbochargers and all pluming etc.. add on weight quickly. However, RX7s weigh around 2800 LBs and in stock form 255 HP are very potent to get. But rotaries require TLC i.e. oil changes every 1500 miles because they naturally burn oil.
Well I'm not going to get one right now. But when I do get one I'll just look at some sites that I know of. I'll probly be getting it about this time next year but ya never know I could get it earlier.