I don't know the numbers exactly, but I recall hearing that Ottawa was a fiasco attendance-wise, and has made NACIS board leery of going outside the US. It's important in the long haul to make the schedule consistent—people with governmental and academic responsibilities, especially those with a heavy conference load, often need to know which conferences they are going to, a few years in advance. Having it always the same time helps maintain a steady flow of regulars. That said, the week after Columbus Day/Canadian Thanksgiving does have its pluses and minuses—I have an annual morris-dance gathering over that weekend that I've managed to not get to for a decade and finally did this year as part of a loop trip... but it was quite a logistical production.
The big question is whether being in a cool location outweighs or at least balances out being in a location that's a little harder/more expensive to get to (and this is true not just for Canada but for locations not immediately adjacent to a major airport, like Duluth, where I'd love to see a conference). Missoula was kind of an experiment in this, and while attendance was fine, it wasn't as good as it was in Sacramento. Then again, attendance was down again this year, and it was in an easy, pleasant, and cheap place to get to. "Slashed budgets" was the best guess about the cause for this with everyone I talked with.
Maybe we could have a different sort of rotating schedule than the one we have (it's very informal, but NACIS tries to rotate around the East, Midwest and West). Maybe we could have one central location we go to every other year, alternating with one less-usual location (including Canada) and just count on a smaller conference on the alternate years that attracts attendees from outside the NACIS core.
The bigger challenge I see is with scheduling. Do we want to allow scheduling NACIS outside of the week after Columbus Day/Canadian Thanksgiving? It will affect attendance, but maybe if we took seriously meeting in co-ordination with other groups, it would be worth it.
I guess I'm on the side of keeping it at the same time, just because knowing exactly when it's going to be helps me schedule other big-ticket things throughout the year. I think the ideal of linking with other organizations is a good one in theory, but in practice, especially in this world of internet blogs and forums and Cartographic Perspectives converting to an open web-based format, the real value to meeting in person is the personal connections. And those are very one-to-one-based, not necessarily helped by shoving "200 of us" and "200 of them" together in a room to listen to presentations. Not that the presentations aren't valuable, but it's the conversations and relationships between the sessions and in the Q&A, the slow building up of a sense of camraderie, one cartographer at a time, that makes NACIS work. IMHO.