One of the best ways to negotiate during conflicts is to refer to objective criteria, and Robert's Rules are very helpful at that. They also provide structure to help keep meetings on track. I think you're asking for trouble to try to say that they govern only when there is a conflict -- and Robert's Rules won't resolve conflicts for you (except over the rules); rather, they provide a structure within which you can resolve conflicts. Also note that if you don't specify a parliamentary authority, your group will be considered by courts (should it ever come to that) to be bound by "general principles of parliamentary procedure" anyway.
In practice, I think most PTOs will use only a very small subset of Robert's Rules, and you don't need to be a professional parliamentarian to follow them. I think you should "call the meeting to order" -- which just means the presiding officer says "The meeting will come to order." That's easy enough, right?
And I think you should make motions and get seconds, and you just about have to take votes -- and this isn't hard either. You don't "make a motion to take a vote". Let's say you think the PTO should spend $100 to buy pencils for classrooms. You say, "I move that we spend $100 to buy pencils for classrooms." Someone else who likes the idea says "Second". The presiding officer says "Any discussion?" Then you talk about it. When it seems like everyone's had their say, the presiding officer says, "The motion is to spend $100 to buy pencils for classrooms. Those in favor, say 'Aye' ... Any opposed?" And then announces the results. The secretary records the motion itself, who made it, and the result: "Sandy moved to spend $100 on pencils for classrooms. The motion carried unanimously." Still pretty easy, right?
As an example of how Robert's Rules might help in the scenario above, suppose you're talking in support of your idea and someone interrupts to argue with you. The presiding officer can say "Sandy has the floor." You can finish, and then the presiding officer can give the other person the floor. This is just like kids raising their hands in class and waiting for the teacher to call on them -- it prevents chaos and ensures that everyone has a chance to be heard, which is one of the primary responsibilities for any membership organization.
Do I think you need to worry about privileged, main and subsidiary motions, or about the proper form of motions to amend something previously adopted? No, I don't. But I do think you should leave standard language about parliamentary authority in your bylaws, and follow basic parliamentary procedure.
