I've never been to SDCC, but I can imagine it won't be any LESS crowded than CIII was. I'm sure it will be a hundred times larger and therefore more aggravating than that was.
Oh just you wait.
There are ways to get less annoyed though (at least I found a few ways).
-Getting to the convention right when it opens is nice since it really is less crowded when you get into the actual exhibitors hall at 10am. It will stay pretty nice for at least an hour or so, after that it will just start to fill up more and more as the day goes on. Plus, if you're into freebies the opening time of the exhibitors hall can be the best time to grab some. If you wait you'll just be fighting crowds of people to get to them later on.
-Getting into the exhibitors hall right when it opens does involve having to wait in a large crowd of people in front of the convention center. Sometimes you can get up to the Sails Pavillion or just inside the convention center which will give you some relief from the bigger crowd outside.
-If they have the movie and TV studios set up in the same area again it will be wall to wall people. It's best to stay away from that area for most of the convention unless you like have to shove and be shoved.
-It's easier to walk around the exhibitors hall solo. I go to the convention with friends every year but walking around with another person (or more) just causes issues I find. Of course, that's just my own personal preference. Plus, as a solo person it's easier to navigate a big crowd. If you're with other people you're constantly having to see if you've lost them.
-If you're interested in getting any autographs on the exhibitors floor you will need to find out well enough in advance when and where they are happening. Most of the time autographs and done by raffle, have to have lined up in time before a line cut off time or gotten a ticket in advance. There are lots of autographs to be had for free but you have to know how to work it to get them.
-If you're planning on getting a sketch from a comic artist and such you'll be waiting in very long wait lines (which is to be expected of course).
-Preview night and Sunday have gotten to be busier days but they aren't as bad as Thurs, Fri and Sat. But perhaps that will change this year. Preview night used to be so laid back and now it's becoming packed.
-Get to panels at least a panel ahead of time. Hall H is the big hall where all the big movie panels happen and it will fill up, so getting to the panel you want to see at least 30 minutes (or more) ahead of time will ensure you can at least get in. Ballroom 20 does a lot of big programming as well (mostly for TV now) and it will fill up so you have to get there early to see panels. All the rest of the smaller panels are hit and miss with capacity.
Don't get me wrong. Comic-Con is so much fun. The crowd issues are very annoying though, but fun can still be had if you just pace yourself and know the areas to avoid if possible during the busy times of the day.
there were all gone ... $115 if you try to get all days ... too much for my blood.
Yeah, I know what you mean. 
