Aside from the cost of getting in to the Rose Bowl Swap meet ($20 before 7am and $10after) It is a pretty good thing to go to. It is huge and is broken up into sections, the middle section is all older stuff, not just garage sale finds but collectibles, the north side is mostly garage sale spaces, lots of clothes and shoes, the section that goes around the bowl itself is all of your new cheap stuff that is new, I generally ignore this part.
I live in Arizona and go to the Rose Bowl twice a year on A&C buying trips sometimes I find alot of stuff (last Oct was awesome!) and other times not so much (the april before bleh!) You have to remember that the Rose Bowl sits in the middle of the Arroyo Seco and is surrounded by some of the iconic Arts and Crafts homes, The Gamble House is less than a mile away and no less than 10 other Greene& Greene homes are within another half mile of that, easily making them walking distance away from Gamble, which must be seen. Then there are a significant number of antique malls also in downtown Pasadena not far away so you could easily spend a day and a half there especially if you are an A&C enthusiast. The prices at the Swap Meet are what you might expect to find anywhere else vendors know what they have but you can always make offers and I have always been able to make a deal on something I wanted. I spent $250 just at the Rose Bowl this last Oct but came home with 8 pieces, a VanBriggle vase, and a Hampshire Pottery small vase amoung the finds plus some unsigned pieces that fit the A&C genre, either way you will see things you have read about or seen in books but worth the money if you are coming from farther away.

Hope that helps!