What cost the Spurs against Dallas in the playoffs wasn't offense, IMO. I'm not sure why anyone would say that it was.
It was a matter of being beaten badly on the glass, stemming from an inability to keep 2 bigs on the floor because of the lack of an athletic 2nd big (that, or Pop's unwillingness to stray from a belief that he needed an athletic 2nd big).
I'm not sure that the Spurs need to find a great deal more offense to get over the hump again. They need to find just a bit more defensive flexibility and a whole lot more rebounding. Ben Wallace would be a wonderful (perfect?) addition to cure those ailments.
Unfortunately for the Spurs, unless Ben decides he's willing to sign for less than market value to play for a contender, he's not coming here.