Canon 24-70 / f2.8 lens needs repair

A friend of mine has a Canon 24 - 70 / f2.8 lens that has been giving her some problems with focusing. She sent it to Canon for an estimate, and they said that the focus assembly and a 4-5th group lens assembly need to be replaced. Their estimated cost for repair is $750. The question is: is it worth repairing if it has that kind of a problem? Or should she just invest in a new lens (which runs for about $1700). She is a professional child / family photographer, so her lenses need to be in tip-top shape. If it is worth repairing, can anyone suggest an alternative to Canon (in the US) that might be able to repair the lens for less money?

Thanks for your input.

--Wendy

Considering how much improved the new version is over the older one I would recommend upgrading if cost is not a major issue.