Clipless pedals - big difference between caged and non-caged?

[flamer]

I need to get some new clipless pedals for my trail bike. I started on the basic shimano spds (M520) which broke and I replaced them with some saint flats for commuting. Now I'm doing a little more riding with mates on weekends - often involving longer jeep-tracks/not very techinical stuff and want to go back to clipless for the long rides. I was just wondering if there is a big difference between caged and non-caged spds pedals eg. M520 vs m530 on the trail. in my mind, if one has a fairly rigid shoe, the only contact point will still be just the middle bit of the pedal.? What are your experiences. I would always want a greater grip/contact point, but do the cages actually provide that?