When should you wipe the dust from your feet?

I attended a prayer meeting last night where the leader read from Luke 10 (The sending of the seventy two). He was focussing on the obligation upon Christians to proclaim the message of salvation, but as he read the passage, I couldn’t help reading Luke 10:11 once again and asking myself how one should interpret this verse in a modern context. According to that verse (and the same message is found in Luke 9:5), if someone working for the Lord is not welcomed in a town, then that disciple should wipe the dust from his feet as a symbol to show God’s dissatisfaction with the town.
I know of some modern evangelists who literally do this. What I was wondering about is when, if ever, we are allowed to do this. I went through all my commentaries on Luke, trying to see what they say about this verse. The “lightweight” commentaries all skip this verse. The “heavyweight” commentaries discuss the verse but give no indication on what the modern meaning of this verse could be. My impression is that this verse is a bit of an embarrassment for Christians.
One reason why I struggle with this is that I am convinced that the gospel of Christ is often rejected because of the way in which we present it, rather than because people do not want anything to do with Christ. A number of years ago an evangelist pitched up in our town with a “monster” truck which served not only as home for him and his wife but also as a studio where videos and tapes could be copied after his preaching (read: performance) and a huge storage room where books could be sold from. Not wanting to rely on hearsay about this man, I went to listen to him on two occasions. There he told the people that in a previous town he had been asked to leave and he had wiped the dust from his feet to indicate that God had withdrawn His hand from those people. Later I found out that the reason why the town council had asked him to leave was because he had been stealing electricity from overhead cables! Now, someone who is rejected for that reason is a far cry from people who are rejected because the residents of a town do not want anything to do with the gospel!
When looking at these two passages again, the one thing that stands out is the mandate which was given first to the twelve disciples and then to the seventy two. In both cases they were told, not only to preach the kingdom of God but also to heal the sick. Without wanting to get into a debate at this point about the issue of healing, it seems to me that the main message is that the disciples were sent into towns as servants of the people living there. Their task was to get involved with people on grass-roots level and to help them with their most crucial needs at that time. My experience with evangelists is that they seldom enter a town as servants. Many enter town, looking more like a film (0r pop) star. Something else which stands out is the accommodation which the disciples were entitled to: Stay in that house, eating and drinking whatever they give you, for the worker deserves his wages. Do not move around from house to house. When you enter a town and are welcomed, eat what is set before you. I doubt whether the local 5-star hotel would pass the test of this passage!
When you have moved into a community, proclaiming the message of peace to those living there, coming in the image of a servant with the attitude to address the people’s greatest needs, indicating – amongst others through your willingness to live as they are living – that you truly wish to associate yourself with them, and the community still rejects the gospel, then we may be able to justify the wiping of the dust from out feet. But until then, I doubt whether we can do it.