Ok, so maybe you want to wait until your spot in Homebuilt Camping dries out just a little bit... but Oshkosh is a great place to visit, even when the snow is a foot deep where you'd like to be parking your homebuilt. Granted, this isn't how the Chamber of Commerce would like you to envision April in the Midwest - but it happens!
One of the great secrets of EAA headquarters is that if you come to the museum at this time of the year, you can have it mostly to yourself - its a quiet place to contemplate some of the great airplanes and read the interpretive signs without thinking about what you're missing at "the show." I often find myself rushing through the place during the annual July sojourn, and I find that I have been missing a lot. I never noticed Ernie Gann's reproduced writing room, for instance - a great place for aviation authors to stop and contemplate one of the great word (and airplane) jockeys of our profession.
If you find yourself anywhere near Oshkosh at any time of the year, this is a great place to commune with the likes an old Standard Biplane, or to think about what it was like to fly around the world in Voyager. Make sure to give yourself plenty of time if you stop by - the real treasures are here to enjoy.