Just to echo what has already been said, don't feel pressed in to using clipless pedals - there are clear advantages if you do decide to go that way, but flats are perfectly adequate with a decent pair of shoes.
I'm also an SPD user - I started off with XT SPD's in the mid 90's a few years after they were released so know them well. I have never felt the need to try 'road' style pedal/cleat systems and have SPD 'MTB' style pedals on all my road bikes - I could be missing out on something life changing

In fact the one bike I don't have 'MTB' pedals on is a MTB

Another benefit of the SPD system is the wide variety of shoes available. I have some carbon soled jobbies that are great on the road bike, I have some ankle length neoprene covered ones that are fully waterproof and fleece lined for winter or off-road use, and I have a pair of specialized shoes that could be mistaken for trainers that I commute in. They're extremely comfortable to walk in and aside from the occasional clip-clop of cleats on concrete you'd forget you were wearing them
