Woohoo, I love talking about head shake!!!
Dampers are not cures, but band aids. You can setup a street bike to be stable enough that a damper is not required IMHO. I ride what is supposed to be the most "race oriented" middleweight (2007 R6) and I have not had any significant head shake. I also run much lower pressure though, 32 PSI in the front as opposed to the 36 PSI they suggest. This probably reduced head shake as it reduced the sensitivity of the front (but adds contact patch). If I do a trackday or start racing this thing I will get a damper for sure.
Have you checked your tire pressure? Remember that even a 2 PSI differential front to rear, ie 36/36 vs 34/36 can significantly change your geometry. A quick ghetto fix would be to run the rear 1 or 2 PSI lower than your front.
What SAG are you running? I would not recommend running racing SAG numbers on the street. The extra SAG and resulting suspension travel keeps that front wheel on the road as opposed to skipping over it. I think 35mm is a good starting point for the front and maybe 30mm in the rear. Too much sag in the rear is bad though, like not enough in the front.
Thoughts from racing:
You know you had a real bad tank slapper when you have no front brakes. I always pump my front brakes a little after a good slapper, something I learned when I grabbed the brakes at 155 and the lever went to the bar. Not cool.
You have to find the compromise between stability and turn in/steering effort. The problem is that the motorcycle reacts differently depending on what you are doing with the gas, brakes, weight etc etc. I try to set the bike up so that I am running minimum damper, but not too stable that I don't need the damper. At WSIR, if I didn't get a huge twitch into T4, I knew I went too stable.
Suspension setup and tires (profiles vs rubber vs construction) can cause head shake all by themselves. The rider can cause headshake too, manhandling the bars or even front/aft position.
Suspension affects loading of the tires. On the gas you can make it worse by softening the rear, making the front harder, reducing SAG in the front etc. Moto suspension setup is PFM as far as I'm concerned anyways.
I never needed a damper on my RC51 until I switched to Dunlop 208GPAs from Pirelli and Metzeler race rubber. I never had headshake issues on my 2000 R6 until I switched to Dunlop 208/209GPA from Michelin PR2/PR5s.
The issue with the Dunlops rears was that they grew with speed, so on the front straight and back straight the bike was getting more unstable. Dunlop suggested that taking out rear compression would stop the back from pushing the front and it helped a lot. The easy fix would have been to go back to Michelin...
Also, I was taught that using the kungfu grip on the bars can add to the shakes because instead of adding damping, you add to the energy. A trick was to modulate my fingers on the bars, kinda like jazz hands, in those places where the bike was head shake prone... and it worked. Don't let off the gas abruptly either because you end up loading the front more.