I would guess that all told the math will help on the strategy front via building the general credibility of AI safety concern

Also, by attracting thinkers who can initially only be attracted by crisp technical problems, but as they get involved, will turn their substantial brainpower toward the strategic questions as well.

For three additional reasons for MIRI to focus on math for now, see the bullet points under "strategic research will consume a minority of our research budget in 2013" in MIRI's Strategy for 2013.