Honestly its like a 1971 transam vs a late model 2010 corvette.
The trans-am is still a way fun car to drive, and its got some solid balls, but it just kinda feels dated. It gets the job done, but not in the same way as the new corvette would. The trans-am really has a place for its talents, while the new vette is a solid performer almost all over.
Being a so.cal desert guy myself, i can vouch for the KX500's capabilities in the hands of a competent rider. I personally love the feeling of the KX500 as a desert bike. Its big, its heavy, but in the desert thats really a good thing. The weight keeps it straight in the woops, and in the fast sections, keeping the shimmys and shakes to a minimum.
Having the KX500 out in the goat trails where you have to man handle the bike does leave some to be desired though. Then again, i would not really enjoy a 2011 KX450 in that conditions either... I guess its kinda finding the proper tool for the job. Thats my take on it i guess.
I thought I wanted to put my KX500 engine into a newer chassis, and i'm glad i did it. But often times I do kinda sit and wish I had not....
My solution is just to find another bike. .