Yeah i get that a walk can be more than just about fitness, it can heal the soul, give you time to think, make you feel more connected to nature, all those good things.
So in that respect it is a good thing. I certainly don't recommend a treadmill - the sheer boredom of it will make everyone but the most determined give up.
However if you actually want results I'd have to say that higher intensity is what you need. If at the end of your "exercise session" you are not dripping in sweat begging for rest, you're doing it wrong, (imo). So like you said if you start running certain parts, that will help. This kind of interval training is a good way to break into running, allowing you to rest after short periods of running. If each time you run slightly more parts and walk slightly less parts, soon enough you'll be running the whole thing and look back at your walking days with a chuckle.
Or just getting a no frills mountain bike and riding your track is a good option, things are more interesting when they whizz past rather than when your plodding along. Not sure where you are, location wise, but searching your local trading paper or something there will likely be a bike for $150 that could do the job. Scope out a few bike shops maybe but don't let them make you buy one one the spot, research a few more options and make an informed choice.
Search youtube for bodyweight routines as well, not sure how you are with pushups/situps and all that but look into it, even if only for a change. Or pick up some light dumbbells and do some routines that sort of blend cardio with weight (low weight high reps) (youtube has plenty of vids).
for example *you would do lower weights as a beginner obviously*:
http://www.youtube.com/watch?v=7kj7WUeqK7c
As for footwear I'd recommend seeking some expert advice here, getting a fitted shoe with support in the appropriate areas would be important, a cross trainer might do the trick, you will know best what terrain you're on.
Or if you go the bike route you won't have to worry about a fitted shoe