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I manage a precinct too. We have a different touch screen system (not Diebold), but it has some similarities. Not having seen the Diebold system, I can't say for sure, but it seems like our system is better designed, but these are still complicated computers that can run complicated code and one must trust the election board. Of course the same was true of the old pin and lever machines and is true of most systems.
Let me address some of your points.
0) I don't think letting campaign workers have the machines at their own house for weeks is a good idea. Of course mine spend a few days in a public library sealed up (like yours), but you can never guarantee that a person with enough resources can't fool with them.
1) This is a problem with any election system. You could take paper ballots, fill them out, and deposit them in a paper ballot box. Or any other way a ballot is cast, you could cast extra ballots if you had the support of your co-workers. If you were really motivated, you could figure out who was not likely to vote (public record) or wait until the end of the day, then forge voters signatures, and cast ballots. That's why (presumably) the campaign workers are at least nominally of different parties. So they won't collude to do this.
So in this case I presume they would count ALL the votes. If the outcome was in doubt, the courts might declare a new election. In any case, they would know who to arrest.
3) If yours are like ours, they have a battery backup. They might even beep at you if you pull out the power. In any case, the votes will be stored to non-volatile RAM and won't be lost if the power goes out.
I think one of the biggest oversights with the Diebold machines is that it sounds like they use a readily available smart card, like something you open a hotel door with. But since I haven't seen one, I could be wrong. In our system, it is a proprietary cartridge that has no electrical contact with the machine. And we never give anything to the voter. We stick the cartridge in the machine and then select the ballot for them (Dem. primary, Rep. Primary, if there are two different ballots in the precinct, etc.) This doesn't make it impossible to hack, but more difficult.