I find that 50 sides gives good representation without adding too much geometry.
I do understand the problem/question at hand, it is frustrating.
When starting an arc you can obviously change the no. of sides to say 50 and create an arc, then draw another arc and Sketchup will remember the last no of sides and use that again which is great.
I tried this earlier by making a new file and drew an arc with 50 sides. Then imported a dwg hoping that sketchup would remember, it didn’t work like that and all arcs were imported with 12 sides.
I would have to change all properties of arcs individually to meet my needs.
I don’t know if there is a workaround but would think it would be able to be added to the import options in future versions?
I tried on 2015 btw