I would indeed call it a filler episode, but that's not necessarily a bad thing. But to say it provides character insight to T'Pol is a stretch to say the least. Really the only bit of characterization we got from her(T'Mir doesn't count really) is that she's nostalgic and isn't above yanking Archer and Tucker's chains a bit. The rest of the episode -does- revolve around three characters that in the grand scheme of things have nothing to do with the series.
Now don't get me wrong, it was a fun episode and I enjoyed it. The Twilight Zone reference was my favorite part, though if the main cast is just going to be sitting at the table, they could've brought in the rest of the crew instead of just having it be the command clique of Trip, Archer and T'Pol and give them an appearance.
Velcro was invented before Sputnik as has been pointed out many times. I figured T'Mir just figured the logical thing to do was con a guy who didn't know better, knowing it really wouldn't change their evolution or technological progress. Knowing what happened to Mestral would be interesting, but dedicating a whole other episode to it would be a bit much.