It takes a lot for me to miss the national! I've never had more than 2 weeks vacation, yet I've make all but 3 since my first in Oshkosh back in '93. I actually made personal leave time a condition of employment when I changed jobs prior to leaving for Durango in '95. The only ones I missed were the 2 left coast rallies and Fredericksburg. Of course being from near Cleveland, Ohio, I hardly got the bike warmed up a few years ago when it was in Lima.
For me the biggest draw is things to see and do along the way to, at or the way back from the rally. Preferably connected by great roads. The facility is primarily only important in terms of the layout, and how easy it is to get from one area to the other. For example, Burlington seemed very disconnected. I thought the rallygrounds this past year was the nicest facility I've ever been to.
Good musical entertainment is a nice bonus; however, there rarely is (at least for my taste). That said, George Thoroughgood put on one heck of a show in Lima! I didn't listen to anything in Wisconsin.
Bottom line is I plan my big trip of the year around the national. Sometimes it takes all of my vacation, sometimes it doesn't. Then I hit as many other rallies as I can get away with.