The important bit in the step for me was 'came to believe'. In coming to believe something requires more than just sitting down and trying to work it out, it takes time. Like anything we learn more by experience, than anything else and with it comes the wisdom behind the steps. For me the coming to believe happened through experiencing the insanity, the only thing that got me on the straight and narrow was attending meetings.
For me, that power in the initial stages was the group itself, i certainly couldn't identify with a concept of God as an entity and have trouble with that concept now. Atheists in AA said how they referred to the group as their higher power so that's where i started.
'Came to believe' for me happened when i would try to stay away from AA, when i felt i could do it on my own, which i have posted about at length here, when i went through those stages in recovery. I found i would go a few weeks without a meeting, something would happen which sent my head spinning, i would then get to a meeting or two, get talking to other alcoholics and share in the group and these acts would in turn 'restore me to sanity'. I had no issue with the fact that this power of the group was and is 'greater than ourselves'.
So for me by experience of using AA when i needed it, i 'came to believe that a Power greater than ourselves could restore us to sanity'.
That power however as well as being the AA group, is now also a spiritual path and part of me that i want to explore. That path gives me peace of mind, or 'restores me to sanity' too.
So for me i eventually come to realise how simple step 2 was, even though it took me many months to get there. We're often reminded the program is 'a simple program for complicated people'.
Paul