It's interesting that you mention Dobbs, because that first scene with him seems like one of the few times Columbo is very open about his "Columbo act" (as it's called). Because he tells Dobbs he'll stop annoying him with the small talk if he cooperates with him.
It's funny that Richard Stahl plays two people from travel agencies, since something like that happened to him on THE ODD COUPLE. Almost every time there was a wedding scene on that show, he played the clergyman.
Hanlon definitely screwed the pooch by not finding out ahead of time that there's no route for the Ding-A-Ling ice cream company to go into that neighborhood. As far as the footprints are concerned and washing them off, if he did leave them a good forensic team would have been able to know that someone else was there. You have to realize that this guy just committed a murder. His brain is not functioning 100%