My update (since I started the thread...) -- I never did find SPD shoes that were "perfectly" walkable, defined as *no* clicking or scratching of cleats on hard-surface floors when off the bike.
Last summer, I put platform pedals on my commuter bike and started commuting just wearing regular tennis shoes. I really, really liked it - and even put the platform pedals on my "good" go-fast bike on some weekend rides when I was going to be off the bike a lot.
But, as summer turned to fall this year, I found that when I ride in the rain my feet were slipping around too much on the platform pedals when riding in the rain. So I switched back to my SPD Defroster winter boots for riding in the fall/winter rain. And I'm using SPD riding shoes in the dry.
Still looking for an SPD shoe whose cleats don't scratch floors when walking...