I'm semi okay with making them wander around, but you do have to remember that it will indeed cause quite a bit of non-literal lag in the sense that you are waiting for all those bots to do their animations. There is also the issue of them stepping on mines and electric floors, opening doors, clearing out cover prematurely, and doing all sorts of other unpleasant stuff.
A simple algorithm would be to say:
1. If bot is not alerted, then "wander."
2. If wandering, look at all four adjacent tiles and see which ones are plain empty floor or other wander-valid tiles (not a hazard, not cover, not doors, etc).
3. If one or more of the adjacent tiles has an opening, then randomly choose between them.
Possible addendum would be to say "don't go back to the tile you were just on unless there is nowhere else to go."
Of course, then you get into problems with other certain bots, like EagleBots for instance. They would have to have their wander logic suppressed.
All told, this could be interesting at some point, but I'm not sure it would add a huge amount, and could be pretty annoying in many ways. I think that a week prior to release is not really the right time to toy with something like this. Press are also getting their review copies starting today, and so this really isn't the time for that sort of thing in that sense.