Absolutely.
Add Carmelo without giving up too much talent or future assets (the Celts keep the 2016 and 2018 Nets picks!) well before next summer.
With Melo on board, Smart hopefully developing further, and a quality cast of role players, the Celts might convince a couple of top tier free agents like Al Horford and Mike Conley to consider signing here.
If the team gets a top 10 pick from the Nets next summer on top of it all, they would be in great shape.
Sure, Melo is not a perfect fit and he may only have 3 or 4 years left playing at a high level. But it'd be worth it because it'd make the Celts relevant and give them a fighting chance at signing some difference makers next summer. Without a star already on board, the Celts have a slightly higher than zero percent chance of signing anybody who matters.