The Evo is definately on the softer side for freeriding. There are two BIG changes in construction from what you have also. NS uses a hybrid design with rocker between the feet and camber starting just past the bindings extending to the end of the effective edge basically. The other change is Vario Grip which is a sidecut profile that adds more edge control through a modifies progressive sidecut with a straight section between the feet. Both work great. If you tend to like your boards soft then the Evo should be a good fit, if you want something a little stiffer for more control at speed then check out the SL or the Proto and if you want something stiff for the most control at speed then check out the Heritage or the Raptor.
All that said- Don't take our word for it. Everybody plays favorites and won't give you a truly honest and unbiased opinion. Nothing can replace the Demo experience. If you have a shop near you that demos NS then ride a couple different models and sizes to find that perfect board. For that matter you should demo other brands and models as well. Hybrid rocker is not for everyone, just as traditional camber, flat or full rocker are not for everyone. For example I like Hybrids and cambered boards, don't care about full rockered boards and feel that every flat snowboard I have ridden were the worst boards I've ridden in twenty plus years of board testing. To each his own.
As for the boards losing there lively feel. Most of the staff at our shop ride NS boards and tally up an average of 100 plus days a year on them. Never heard one complaint about the boards losing their lively, snappy feel any faster than ANY other board made of wood and fiberglass. I personally rode a Legacy in a pinch last spring that had months of heavy rental use and found the board to be quite lively and snappy.
Hope this helps out!