I nearly make a week of it now. Last year I flew in on Monday evening, went to the Master Measurer's course on Tuesday, and attended the show Weds-Sat in its entirety, flying home Sunday. I've done it in years past where I flew in on Weds or flew out on Sat evening, but it makes for long days and I feel like I'm missing out on the show. This year I'm flying in on Tuesday night and home on Sunday. Go to one or two of the SCI events in the evening. They usually have great entertainment, and the auctions are something to behold. The seminars are great for the first few years you attend, but they get old quickly because they don't rotate/refresh much year to year. I'd suggest booking a hotel now, and if you want to have a special meal at any of the popular restaurants, make reservations as soon as they're available. 
Wear comfortable shoes and a large wallet!