Neo,
I just retired my 1990 240SX/180SX with 230,000 miles on the odometer. Needless to say, I put it into REAL good use. I'm only the second owner and drove it for the last 6 years.
I can relate to what you're saying about the similarities with the NSX. I never said it before because I might have been flamed for it. But since you said it first, I'll just hide behind you.
The looks, the feel, the handling, even the reliability are all similar. Not the same, mind you. But very, very similar. I would go far as to say that the 240SX is only a notch or two below the NSX in that respect.
The modifications available to the 240SX is widerange and with the proper installation, it has every potential of becoming a beast. Especially, if you do an engine swap with turbos. Those are illegal here in the States but a lot of owners do them anyway.
If you can't wait for the NSX, get a 240SX/180SX now. If anything, at least it will give you a feel for what you can look forward to in the future with the NSX.