I had an s13 silvia track car (yes, I admit, it never actually made it to the track due to it's 10 day life) and I just wasn't happy with the look of it (it's a chick thing!) , everything else was absolutely fantastic! The engine was an SR from a s14, it was a little less torque that i would have liked (but i was coming from rb25 land) but I'm sure that can be fixed without too many dramas.
I now have a 180sx being put together with all the same bits and pieces that were on the silvia, it'll be interesting to compare the two, but I'm in love with this 180 for the looks alone!
I guess the thing with the s13s is, aswell as it being a light, and perfectly balanced car, it's been done before.. you name it, someones done it... in terms of modifications that is.. the ideal handling set up might be a little bit harder to find though.
without having driven my 180 yet, this is SOOOOOOOOOO good to hear!