My first pistol was a Compact 16 with a rail. Solid all steel gun, decocker, all that jazz. I never had the D spring, but if I had kept the gun I would have installed it. Only sold it because it was an impulse buy on the way to a gun I really wanted... problem is, I liked it and plan to buy a new one to replace the one I sold (bought it used). Never one single malfunction in around 400 rounds. The D spring and a low profile safety are the 2 upgrades I would suggest, I'm not a fan of the Beretta style safety, but that's just preference.
There is also a pretty long thread discussing this topic in here somewhere. I did a quick search but couldn't find it.
EDIT: AFAIK All the yavuz models are admissible in Production class IPSC.