SEMA is a blast, its mainly a trade show so there are a lot of vendors and such, but pretty much everyone builds or brings vehicles to show off their products or services, its also fun to see the concept car unveilings... its industry only so you need to have a reason to be there to get admittance, I get to attend on press credentials, and everyone there LOVES the press because they get to show off all their project cars and products and stuff to the public...
Speed week is unlike any racing event you've ever been to. its so completely laid back and relaxed. The vehicles are racing against themselves and records, so its not like any head-to-head competition...they're just trying to go as fast as they can...they let everyone go pretty much where ever they want, pits, starting line, etc...and there are some strange and interesting vehicles there, pretty much everything is done by hobbyists, amateurs, and families so everyone is super friendly, and they love sharing what they've done....I'm lucky I live about an hour away from the salt flats, so its really convenient for me to go.