I have a 2013 Leaf S, I'm reading on here that the 2013 susp is either stiffer, or stiffer as a result of the weight reduction on the 2013 model. Either way, I think my car is reasonably firm for what the car is marketed as. That said, I would also appeciate a little more stiffness in the rear which can normally be remedied by a rear sway bar, but in the case of the Leaf with a twist beam axle, this isn't an option. Installing a full coilover setup is not my deisre as I'm not into lowering the car more than maybe an inch, but I really don't want to chase down a custom rear spring setup and the only aftermarket shock I'm seeing for the rear is a KYB GR2 from Tirerack which have typically been 20% stiffer than OEM shocks. They're cheap on there at right around $50 ea. I would just need to find a rear spring then that is OEM height but with increased spring rate by 20%...but I don't think that is going to be available in my searches, so I'm stuck with taking weight out of the rear of the car, which is not my ideal solution to firm up the rear. Don't get me wrong though, I am a weight reduction freak, but I really don't want to have to remove the rear seat & trunk trim to accomplish only a minor gain in rear stiffness. If I didn't have a wife & 2 teens, I'd have already done it tho! Lol.
What I have done, and I've chronicled it in the accessories/mods section recently, is add some 17x9 +35 Enkei RPF1 wheels and some SPC camber bolts (which have increased front grip). The grip level is amazing, but it is a bit disappointing because I KNow it could be even better.