A few of my thoughts. Looking back a few years, the MVPA Annual Convention dates have varied while the Gathering seems consistantly the first weekend of Aug. Speaking for my own self, I appreciate any group that holds an annual event keeping it at a time slot I can count on well in advance.
While I agree that it would be nice to get everything together in one place (or at least not have competing events within a given market area) I would suggest that the GT bunch have their Gathering more like a reunion than a public display, ie, getting the word out is important, but it seems to me it's more about the comraderie amongst the GTers. I hope I'm not speaking out of turn here, these are my thoughts based on my observations from the 2010 Gathering. I'm sure PB or Driver will chime in.
I don't think that the way things are scheduled for 2011 will have a major impact on either event. Again, speaking for my own self, I'll be at the Gathering if at all possible but have no plans to attend the MVPA convention unless they have it closer to the NE.