I Think this winning culture thing is way overated, and half this roster might not be here next year anyway. I hope this team makes the playoffs though because finishing in ninth place is the worst outcome for this team.
This is sort of where I come down on this.
The Celtics are on the cusp of being in the playoffs, cusp of just missing the playoffs.
Think of the choice as between these options:
(1) Take the #12 seed (which is where I imagine the Cs end up if they miss the playoffs).
(2) Take the #17 pick (which is where the Cs end up if they just make the playoffs).
Note that (1) gives you a ~2% chance of earning a top 3 pick in the draft, a 94% chance of ending up with the #12 pick and a 4% chance of earning the #13 pick (that's right, you have a better chance of moving back a spot than you do of moving into the top 3).
Note that (2) gives you the #17 for sure, some playoff experience, some extra run for the youngsters (potentially marketing them as trade bait for a draft night trade or summer trade).
All else considered, I think I go for (2).