Carb synch, plugs and seafoam sound like a solid start to the trouble shooting, also make sure the original owner did not remove the weights on the ends of the handle bars, if those have been removed the bars can get some vibrations in them.
As far as lacking get up and go, remember this V-4 like to produce power at high RPMs and both 4th and 5th gears are overdrive gears. If you are tooling along at 65 in 5th gear and try to accelerate quickly it will not respond like a V-twin. If you to get out and pass someone or just want to go faster quickly drop down to 4th or even 3rd and give it some gas. The bike actually performs best in 3rd gear, if you have not tried it, get on the road and while in 3rd gear, give as much gas as you like it may surprise you how quick it is.