I think asteroids should be a threat, depending on the speed of the starship and the nature of the engagement.
asteroids felt neat to me on the way to a battle, but they always drove me nuts on the way back.. there I am venting plasma from a half a dozen holes in my ship and I run into a little rock.
then I got to do it over again.
It all depends on the individual field. Vega and Enigma are just rockier than the other sectors, I suppose.