Jamie haven`t got personal experience but,this is from John Tipplers book on the Spider.
"If you were set on uprating its undoubtedly fine handling,you might fit a set of Spax or Koni dampers with harder settings at the front and softer ones at the rear."
He also reccomends lowering which he says along with getting the tyres right "is the single most significant improvement you can make to a standard car.
A mate had a modified Sud and he tried Spax but ended up with Koni adjustables,after getting advice from Alfatech in Luton.
EB spares in Westbury might also be able to help you on this one,as they do handling mods for Spiders.Hope this helps.
Some days you`re the statue and some days you`re the pigeon