I did indeed go along to dinner afterwards and, eventually, had a chance to speak to the guest speaker. It was so good to speak to someone who actually knows the ambient material surrounded my dissertation topic - I so rarely have that opportunity. He's promised to email me some useful followup dissertation. Between that conversation and the one I had with my advisor the other day, I feel as if I'm filling in many of the gaps I should have already known, but it's just as well I know now before my dissertation is much further along.
If you're in the right city, he's giving a talk on "Time and Scholasticism" this Friday, 8pm, Rm 100, Alumni Hall, St. Michael's College. I recommend it.