I think an element of cheering for a team yet to reach "consistent contender" status is this anticipatory feeling you describe.
I feel the difference between us and the Sixers is that we are not apologists of losing. The Celtics try every season to improve, and put out a product that is enjoyable for fans to watch. We may be constructing the equivalent of an NBA mid-major, as a few posters have suggested. However, I feel we can at least take pride in the fact that we try to win.
To me, that's a big difference.
TP. Right now, I feel like what Ainge and Stevens and the Celtics are trying to accomplish is very transparent.
Of course, they'd love to make the big deal that puts us over the top and vaults us into contender status. However, those deals are rare and they aren't guaranteed. In the meantime, they are trying to build a team that plays hard, plays smart, competes without having big superstars, and makes the fan base proud of them.
I'll gladly take that for now. I'm lucky that I've never felt that every year that we aren't a legitimate title contender is simply a wasted one. I get excited for every Celtics season and am looking forward to next year's where we enter as a scrappy, young, up and coming, team oriented squad that will have a good chance to win at least half our games and be among the top eight in the East yet again.