What I have:
I purchased a 2-3 year old Craftsman 11/30 for $350 a few months back. I use it at a hotel clearing the sidewalks and going curb edges in the parking lot (if I don't do them the plow guys leave a mess there), it has done relatively well. I would NOT recommend it for commercial use only because it uses a 1/2 size belt (37.5ish inches long) so I cannot get a kevlar belt for it and have to use an automotive belt. Otherwise, I could recommend it or something like it for backup clearing sidewalks. I tried a track drive one and was not very impressed. Not worth the extra $ to me.
Drive system:
Are you looking at tracks for the traction? If so, I would recommend instead a machine with steering brakes. I have never needed more traction than I get from the "snow hog" style tires and the only complaint handling wise I have had is that it is hard to turn on the sidewalk when the tires are locked together.
Size:
Having a 30" machine and clearing 60" sidewalks, there are times I wish I had a 32" blower as I cannot get it all in 2 passes, if you are getting this to clear driveways as a backup I would go with a 32" or larger blower. Otherwise you will be blowing for a LONG time.
Other Options:
Have you thought of getting a 300-400 series Deere with a blower/blade and a cab? Something like this perhaps? It could still fit into a truck with the right ramps but would be faster and more comfortable to use than a walkbehind. Another option what I would like to have is a front mount mower like this. Either could be used in the summer to mow and act as a backup for wintertime.
You might appreciate the cab and being able to sit down in such a situation. I know that walking behind a 11/30 craftsman wears me out quickly and I am only doing the sidewalks for one building.
Just my $0.02
Aaron Z