Allah Pundit weighs the pros and cons:
She needs an issue, and this one is fairly low-cost with a few major benefits. Taking a modest pro-legalization position (i.e. “I don’t use it myself and don’t want kids using it, but…”) would (a) electrify the debate over a hot-button issue, which she obviously relishes doing (see, e.g., “death panels”), (b) prove that she doesn’t mindlessly follow Republican orthodoxy, which would force centrists and libertarians to give her a second look, (c) mindfark the media, which would be on her side for once, and (d) reestablish her political identity as a western, not southern, conservative.
My position on this issue was hammered out in a debate with Mary Grabar that can be read here and here.