One thing is do one time succesfull 51% attack to doublespend your coins only one or few confirmations back which will not make huge impact on Bitcoin price. But if it was continuous attempt to mine all blocks for yourselves with 51%+ and refusing adding on top of other blocks or double spending often at will any number of confirmations back, then this would crash Bitcoin price a lot - so the attacker will have worthless coins, but I can see why someone could attack Bitcoin for ideological reasons this way especially when he could take control over the mining equipment basically for free like China government.
So yes, if you have few coins stored, consider running one ASIC rig even at financial loss at very small nonChina pool or P2Pool.
The most critical event is if the attacks are combined with a big (short-) selling action.
So If anybody here knows proper risk evaluation & modeling processing (not only market-risk !) you'd see what I'm about here.
Any risk that you see front up you need to calc & minimize properly -> that combined one is the biggest I see, but looks like one can fix it. I do NOT know how much money you Need in order to do.
PS: Everybody here needs to do own risk management.
