I was wondering when you guys run errands (grocery store, target, wal-mart, etc.) if you wear cycling shoes to walk around inside of the store. It's a pain to carry a pair of shoes just to walk around a store for maybe 15-30 minutes and then get them to fit in my cheap crappy pannier stuffed full of groceries.

Besides accelerating cleat wear (I have mtb shoes so the cleat is kind of recessed), does walking in cycling shoes harm them in any way? Such as wearing on the stiff sole, etc.?

The shoes I have are these:
http://bontrager.com/model/09152

The only reason I'm so worried about them is they were super expensive (90 bucks from LBS). I know there are much cheaper shoes online, but these are my first pair of cycling shoes ever and I wanted to try them on before buying. Thanks!