Re: May I come visit your dojo?
When I trained at Chiba Sensei's dojo, we had visitors, from everywhere, with all kinds of rank, come on by to train. Some came for a while, some came for one day. Before that I trained at two Western Region dojo (Chiba Sensei affiliated) and again it was the same thing - all welcome, always.
I think allowing visitors into one's dojo is not necessarily about trying to gain something from them directly. It seems to be more about what we as a group and as individuals gain (and learn) as we take on the responsibility of host. As we understand this responsibility at our dojo, we don't have a mat fee, etc., and we try and do a lot to fulfill this role of host as fully as we can - even providing food and board whenever needed. For us, we don't take on this role of host because some visitor is going to or can teach us something we don't know and/or should know. So, personally, what I try and do is to take the role of "host" as seriously as I can. I wouldn't consider myself being serious regarding the benefit of hosting visitors because I turn away a lower rank/1.5 year old practitioner.
I'm not out to try and tell anyone what they should do, and certainly not what the dojocho in question should have done - to each his/her own. This is just more what we do and have done.