I think cory is right, its the bigger motors that have the most gain. 90% of the VE's out there are stock internals. The other is if you can get a set of N1s for $500, and Kelfords are close to $1000, is it worth the 3-5HP you are gaining. To the majority it is not, and N1s can be even had for less which makes them really attractive. For the few that are pushing the envelope Kelford is the only one making any sort of advancements, and we all have to be glad that someone is.
If you think about the N1s, they were designed for a race motor by Nissan, i would love to see how much R&D they have in them. Now look at it from another companies view, how much is it going to take to greatly improve the design for a 2.0-2.1L VE? How many sets are they going to sell? Like others have said, this is a dying motor and car so support is not going to go up much, although the VE has more support than ever, it is probably hitting its prime.