A big reason KG ultimately okayed a trade to Boston was that the Celtics had Pierce, and then Ray Allen. So at the time of the trade for KG, the Celtics had:
Paul Pierce
Rajon Rondo
Kendrick Perkins
Glen Davis
A couple of trade chips they used to get Ray Allen
Al Jefferson, Gerald Green, Theo Ratliff's expiring contract, and a high draft pick, plus a couple of role players, for KG
After that, they signed as free agents:
Eddie House
Scot Pollard
James Posey
So,even though they were able to trade for KG,the Celtics had enough talent at the time to:
build around a great player (Pierce),
draft and develop enough talent to keep or use in a trade,
collect some draft picks to either draft players or use in a trade.
then collect enough core talent to convince some veteran free agents to sign there as role players.
Right now the Celtics don't really have that much talent. So they just have to keep drafting and developing players until they get one they can build around. I don't know how good Smart and Young will be, but they'll either be a part of a contending Celtics team or be traded for a player who puts them much closer to contention.
This is one reason I think a trade for Love wouldn't be in the Celtics' best interest. They just don't have enough talent to give some up in a trade and still have enough good players to contend with Love. However, in a couple of years, when some of the younger players have progressed in their development, the Celtics will have enough assets to make such a trade. And I think that is what Danny will do.