I saw your ad and thought it was a bit soon to give up on it. I'm kinda glad you're giving it another chance.
IMO, the 919 can be had for a few grand less than others like the ZRX, Monster, Buell, etc...
I also have an opinion about mods and it lines up with what you've said about not fully utilizing some of the more expensive things.
When I got mine, about the 3rd year it started acting funny. I finally got around to reworking the forks and they were a HUGE mess. There was water in the forks.
Point: before you start getting into mods, I'd go thru things.
Some things you can't go wrong with, like tires. Get the greatest tires you can, rebuild the forks, adjust the suspension as best you can.
At that point, you haven't wasted any money.
Look at things like gold valves / springs or convert to something else like the F4i or whatever.
Some have had the rear shock rebuilt, or replaced with another, plenty of write ups on that.
One thing that we really don't seem to have (or that I can find) is how to dial in the suspension. I've seen videos about ride height, but really can't find the info on adjustments.
My point is that you won't be wasting money on great tires, rebuilding the forks is cheap and might get you where you want to be.
I'd do this before you look at mods because mods tend to cover faults.
If you happen to come across a great tutorial on setting up the suspension, share with the rest of us.