I don't believe applying for both position would be viewed as a negative. If it is questioned you can respond similar to what you did in your post. It would show that you are interested in working for them at that particular facility. Just don't hide it and attempt to play them against each other. Be honost and upfront about the reasons you applied for both.
At our facility Operators are on shift work. I&C Techs are straight days. I&C is union. Operators are union until they become shift supervisors / shift managers. Here, because of shift work, stress/pressure, ops requal and pay I&C is the more desired position. It could differ from plant to plant.
In regards to advancement positions, I think both offer advancements. Now with scheduling, planning, procedure writing, supervision positions, etc grabbing bodies I would think once your in you can determine your advancement path.