In the end, the geometry and gearing of the Sirrus were just too big of question marks / negatives to go for it, despite the great price and how much I liked the bike. I was leaning towards the Lucas Valley until I happened to find out a local shop was selling the Mill Valley (one step up) for $890 (only $90 more than the Lucas). It was in near mint condition, too (the Lucas at the other store had been out on more than its share of test rides, I think).
Took it out for a spin, and we had a winner. Exactly what I'm looking for as my commuter, including improved components over the Lucas, and I've decided I likely will never carry more than ~25 lbs worth on a regular basis, so the seatpost rack should work fine.

Thanks for all of the input!