The IST isn't going anywhere.  It brought eyeballs and revenue, and the players were engaged.
I'm not sure that one extra game is to blame for the Lakers / Pacers slumping.  Maybe they're just unfocused teams that needed a short-term goal.   The Lakers have played 30 games (29 regular season, 1 IST final).  The Pacers have played 28.  That's in line with other teams, such as the Jazz (30 games), Cavaliers (29), Nuggets (29), Pelicans (29), etc.
I don't think the Celts would be playing significantly differently if they'd had one extra game at this point.
The trophy / banner is meaningless, but it's nice to see the players occasionally exert effort.  If the team is pushing for regular season wins, that will pay off in seeding.