They're advising snug, and it looks like you're planning to do just that -- I got my first bike shoes when I was still using those toe clips/cages because "normal shoes" -- and I think crocs would fit into this category in this case -- had my feet hurting something fierce when I rode! (btw, if the shoe doesn't go into the cage and you have to be on top of the cage, then there's no point in having the clip there at all!)
DH loves the Keen commuter sandals -- he's got a pair of those and one of "regular" MTB shoes, and even in February he doesn't get out the closed shoes!
You'll find a world of differnce just wearing the hard soles, and when you can actually clip in -- whether using the cage things or the cleats/special pedals, you're going to be amazed!
(I had to get new shoes last spring, when my old ones were too big and my feet slopped around inside something fierce. Now, I can still wear the ones I bought last spring, but SIDI had those cool floral road shoes out in a pretty blue that would go so nicely with my bike and helmet, that I'm just incredibly tempted!)
Karen in Boise, who's reluctantly getting ready to put away the ski boots and get out the bike shoes -- one tight fit for another! -- for the summer season!