Regardless of what school you go to, if you do well in your classes, get a good recommendation from a big name (or two!) in your field, and get some first-author publications, you will get into good grad schools for biology/chemistry. However, the difficulty of Caltech prepares you exceptionally well for graduate level coursework, and the huge amount of cutting-edge research going on here makes it pretty easy to get the experience that graduate programs crave.
While you can get a SURF at Caltech while going to another school, it does seem to be harder than getting one as a Techer and you'll be missing the contact with professors that you would be getting from classes here. You also lose the ability to do research during the school year with whatever group you want to work with.