Bilstein shocks with factory everything else, or with the Hotchkis setup. Or Bilstein PSS or PSS10. The factory shocks suck compared to a quality aftermarket shock. Most of the ride problems can probably be solved with $700 on eBay for Bilsteins.

 

+1 on a few of the comments:

Smaller diameter wheels with higher sidewall profile tires (17" but 18" should be fine)

PSS9's are a good option for suspension (which would be one of the main components that affect ride quality), but better yet are KW V3s coilovers which comes on the Mercedes CLK63 Black Edition as OEM suspension. Can't get any closer than that

http://www.kw-suspension.com/en/



PM if interested since we sell them, but you can also find the KWs from many other distributors as well.

 

there you go..

 

I just joined 350Z.com so I can answer this.

Back when I had my yellow 2005 350Z Anniversary Edition, I found the ride horrible, so I fixed it. I disassembled things and found the struts/shocks to be WAY too stiff. So I knew those had to go. I also wanted to change to softer springs. I am an engineer and had autocrossed for over 20 years at that time. Here are the things I did to fix the harsh ride...
1) Changed to a softer riding tire (From The Tire Rack, I bought 2 sets of the softest riding tires in their various tests, mounted both, then used the softer ones and sold the other set). This got rid of 50% of the harsh riding problem. I could not change to 17" wheels (or I would have) because of the Anniversary large brakes.
2) I changed to G35 (sedan) springs and shock/struts I bought off eBay. The front strut was modified by taking 3/4" off the steel rod extension potion. Everything bolted in from there. Ride height was as stock. These spring/shock-strut change solved the other 50% of the harsh ride.
3) For 5% more help, I changed to 2003 sway bar(s). They are smaller. I can't remember if the rear has a bar, but I do recall I changed the front. Smaller sway bars reduce harshness when 1 wheel goes over a bump, but the other one does not, so this is an important step too.
The above changes made the car tremendous, ride-wise. And because of the low CG of the car, I found the softer setup had almost no impact on the handling abilities.
Unfortunately 2 months after I finished the car my company sent me overseas, so I had to sell the car because I had no way to store it. I'd like to buy it back if I ever find it!!

 

Custom valved konis with softer springs. Also, as pointed out earlier, 17" wheels with 50 series tires.

 

Wow, necro-thread bump.

Honestly don't see a point of trying to soften a Z's ride. Taking out the harshness and controlling spring oscillation in favor of a more controlled ride, yes. But softening? Wrong car.

If one wants to truly "improve the ride" (in the above scenario) without going to the extremes the thread bumper did, go with Bilsteins on stock or mild springs. These will smoothen out the transitions between varying road surfaces and control the springs better than any other shock out there.

Even my standard valved Koni Sports on medium setting give a much less harsh/jarring ride than '03-04.5 stock suspension - which just sucks.

No, none of these things will ever make a Z33 "soft" but satisfying in its relative firmness, oh yeah.