Durability of Seat and Chain Stays on steel frame touring bike I've been toying with the idea of mounting a dynamo on my REI touring bike. Model is ADV1.1 and it has a steel frame.

Dynamo attaches by a mechanism that clamps onto a seat stay and tightens with two bolts, but I also recently got spooked by stories here and here that similar mechanisms for kickstands run the risk of crushing the chain stays.

I don't have much experience with mechanically modifying bike frames, so how generally concerned should you be about fixing things to or modifying a bike frame for fear that it is damaged or weakened significantly?

And how much should this concern vary between different brands or types of bike, i.e. touring, mountain bike, etc?

Should the concern for kickstands and the chain stays carry over to the dynamo scenario?
Situations when the weight of whole bike + cargo (+ maybe a rider?) is concentrated on a small patch of kickstand's clamp and when a small dynamo clamps the same seatstay are really incomparable. In the first case it's a thousand Newtons of stress applied to a piece that was not supposed to be pressed in that direction, and for dynamo it's about five Newtons and the clamping force.

I would say just clamp your dynamo mount with a reasonable torque, or, if you are really paranoid, use a torque-measuring wrench and clamp according to manufacturer specifications. If it turns out to be loose at some point, simply re-tighten it.

Steel and aluminum alloy frames could sustain quite a lot of abuse of excessive clamping torque (but there is no need for it in the first place). If you make a mistake and instead of 4 N×m would crank it up to 20 N×m, it will still be OK. But I doubt that you will be able to achieve such huge torque with a typical size 3-6 mm allen key that is most likely used for the operation.

If your frame is carbon fiber, then a more accurate approach is recommended, as this material is more sensitive to clamping. However, I am not sure that there are many touring carbon bikes around.