Yes a ZX14 has a lot of potential. Just buying performance parts will get you some gains but may not give you all the reliability unless you start spending more for the parts that need upgrading for long consistent use. His bike can handle 400hp with Nitrous,with lower compression pistons 400hp with a turbo. That's in the engine and the transmission. All has been upgraded.
He doesn't have all of the best parts but damn near it. He was never going to push it beyond 300hp anyway. We were close though on one of our dyno pulls.
A nice street bike and a track bike is sometimes the best way to do it. Especially if you don't really street race often.
It's sad to put so much money into something and then eventually sell it for a fraction of the investment. IMO, at least go out and use it as much as possible to get your money's worth. He just never really ride it that much over the years. I think he has an actual 12k on his bike. With the sprocket change it will obviously be higher on his odo.
This is why I approached you as you will make good use of it. Trust me, we want someone we know have a chance to utilize this toy.