Why destroy the station in the first place? Besides didn't they tow Empok Nor into the Bajor System (it was a DS9/SCE crossover)? Couldn't they have just activated it and had it become Deep Space 9-A?
They ripped out the old fusion cores for DS9, since those were ejected when they overloaded thanks to sabotage early in the Relaunch. Cardassia couldn't supply new cores since their entire industrial infrastructure was messed up after the war.
As for a new station being build, if you read the books, it was made clear it was as much a symbol as a necesity. To show the Typhon Pact that the Federation won't be bullied down, and that they will rebuild. I think you could almost compare it to what the new Tower being build in New York. To rebuild exactly what was, can open up old wounds for some. But to build something new, something out of the ashes so to speak, is a powerfull symbol for some.
And they still should have build two towers, not only one.