We've been going for a few years, have never gotten badges or wristbands, and have only a handful of times been turned away from shows we wanted to see (and then only because of our poor timing or indecision.) If I'm not mistaken, when you get a badge you get near-guaranteed access to every show. People with wristbands stand in one line, people who want to pay cash stand in another, and badges generally just wait in line long enough for the doors to open and then walk right in. I'm sure this isn't always the case, but you should get into nearly anything you want to, especially if you get there at a decent hour.
We've really enjoyed it in the past and have seen some great shows, but we have other business in Austin that made it better than it would have been had it just been a music vacation, and we live not far away. So is it worth it? Probably, especially if you've never been. Just be aware that the city is fucking overcrowded, people act like assholes, and sometimes things that sound like they will be great end up sucking (while things that appear crappy end up being great.)
The only advice I have is to drink a whole lot of water. I always feel dehydrated at SXSW. Park by Progress Coffee just east of I-35, and walk to 6th/Red River/wherever (there's nearly always free parking there on 4th and 5th.) Go to the Oklahoma-only showcase at Progress if you have time, 'cause we're all real cool, or just get coffee there because it's pretty neat. They have a great happy hour, too. Read
http://donewaiting.com/category/sxsw/ and
http://showlistaustin.com/ as the week approaches to find out about who the "Special Guests" and "TBA" really are and to find out about day parties/promotions/etc.
Oh, and DO NOT eat at Mekong River on 6th street, unless you want to spend an hour in a portapotty in the Emo's parking lot during the Secretly Canadian showcase, only to run into (literally RUN directly into) Craig Finn with "I just spent an hour in a portapotty in the Emo's parking lot, howsabout we make out now?" face. Don't do that.