Welcome to the board. I'm a gen II owner who looked at both cars extensively before I chose. Let me take a stab:
I am currently looking for a used CS. I have a few questions and would appreciate feedback.
1. Is there a noticeable difference in performance between the Gen I and Gen II? I would appreciate comments from someone who has driven or owned both.
For me, there was. The first time I drive a gen II car, I really wanted one. This after I had convinced myself that I wouldn't consider one. Many gen I owners will say that with a few quick mods, you can equal or surpass the power of a gen II car and they are correct. The downside is good luck getting warranty if your engine blows. I wanted a drive train I could leave alone and track as-is.
2. I have been researching on this forum and it seems inconclusive whether PASM is a must have. I think that I should concentrate on just looking for a good example at the right price and not worry about PASM.
It depends on what you're used to ride-quality wise and what you plan to do with the car. If you are strictly a street driver and find the car a little firm for your liking, definitely opt for a PASM car. It is a little softer and the ride quality a little better. It also gives you a firmer suspension if you like it for the twisties. If you are a track guy, my opinion is go standard suspension (as I did). So far I've found it pretty impressive on the track and when the time comes to upgrade to a set of coilovers, I won't have 4 very expensive paperweights in the garage. Best advice is to drive both and consider what will work for you.
3. Are there any reliability issues that were addressed in the Gen II CS?
Yes. The rear main shaft (RMS) and intermediate shaft (IMS) leakages and failures were completely fixed in the DFI motor. So far, two other significant problems were also addressed in the DFI cars: oil starvation in high G situations (tracking) and power steering line/pump failures due to heat (also tracking related). The feedback on these fixes comes from the Cayman Interseries Challenge cars which have "performed without a hiccup...for 30K aggregate track miles". If you don't track your car, these things are much less significant though.
You may also come across a thread discussing the DFI motors and carbon buildup. AFAIK, there has not been one reported case in a gen 2 Cayman or Boxster to date. Personally, I think it is unreasonable panic but it is something to consider.
4. Any comments on the Sport Chrono and Sport Exhausts would be appreciated. I wanted to see if I should look for an example with these options.
Many say sport chrono is a must. I personally do not. Again, if you track (see a pattern here?) SC gives you higher thresholds before PSM (stability control) kicks in. It also gives you sharper throttle mapping. It also gives you a big wart on the dash. The first two functions can be duplicated in the aftermarket (Softronic Flash) if you find the right car without it. Sport Exhaust is a really nice option. It gives you quiet when you want it and throaty when you want it at the press of a button. What it doesn't give is any performance increase. If you're looking for that, aftermarket exhaust is the way to go.
If you have any other questions, post up. Best of luck to you.
Thanks.