Theres always room for better handling, but more HP is a big debate. I suspect it is based on what it is you do. If hill climbs and sand drags is your only cup of tea, then have Fredette design you a nitrousoxide kit..LOL In terms of riding regime, I think its the quality over the quanity that will serve the "recreactionally time challenged" best. Putting around is ok, but sme form "riding scrimage" is a good, time effieicent means of refining and sustaining your skills. Every time I ride, be it the track or off road, I spend about 10-15 minutes doing figure 8's. It sharpens my braking skills, reminds me of proper body postioning, etc, and serves as a good warm up. I feel that a bike that is inherently easier to ride, will for most people be the better choice. Thats why on occasion you see riders competing in events with bikes that are theoritically slower. IE, racing MX on XR400 or a high end enduro bike, like an EXC. And yet, quite often these riders do well. Why? Becuase the component most often over looked in the equation is the rider. This isnt car drag racing where the vehicle does all the work. Motorcycle racing involves the rider as an intergral component. As such, the rider must match the skills of the bike. As you get older, your ability to react slows. Riding a bike that it too demanding and requires constant seat time just to control it isnt a sensible option to me. I think thats why as of late, you see so many older vet/senior mx riders involved in horrific accidents. Part of it is the tracks design of course. This by the way isnt limited to "40 somethings." Being 16 does not not in itself make one a factory rider. Without digressing too much, let me say that for me, with my mediocre skill level, a refined KDX is enough.
In closing, I was educated by a recent college grad, who earned her degree in some type of sports education discipline. She spoke about the theory of reaction time (the biggest enemy of the "aged") and its applicabilty to sport for the average joe. In essence, instead of trying to master a large amount of techniques for every situation, focus on a few, versitle moves that will work for most situations. As a result, there is less information for the brain to categorize and review in the heat of the battle or race.