I think you're trying to solve a problem that won't be there as you get more seat time. The 250 does fine on the highway and I think you're just not used to it yet. Better tires offer better grip which is used to cornering, not really for freeway speeds. Better tires typically wear out faster too because of said grip.
IMO, a steering damper is a waste on a 250. Have you played around with the preload yet?
http://www.ninjette.org/forums/showthread.php?t=11956
It's free and it can make a huge difference in handling. If you're in your first few months of riding, don't change anything yet (unless cosmetic). How you feel now will change as you get more miles under your belt. You might change something out now and then realize you like it better stock.
