I think both sides of the argument are correct in this case. This game is just 1 of 82, and we're just getting into December. We have new pieces, and Spurs history shows that new players are notoriously slow in assimilating to the "Spurs Way" of playing. And obviously, health is the biggest need for this team entering the playoffs (I'd take a healthy 6-seeded Spurs team over a #2/#3 seed without Manu).
However, if our goal is a championship, we should place some emphasis on the teams that will be standing in our way to that championship. Boston is a legitimate le contender. We only play them twice in the regular season. This is a measuring stick game, not some game against Chicago or Oklahoma City. Pop has had nearly two full months (preseason and reg. season) to tinker with this lineup. We're not a finished product by any means, but we aren't fresh out of the box either. How we play on Thurs. should be taken as (somewhat) indicative of how we would matchup with these guys later down the line.