Definately do a drop u will be ridin a monster truck if u dont lol. I would invest in coil overs if u got the money and the plans. I'm goin balls out on my mustang now and Im loving the modding process.
DO NOT ! get coilovers they are not worth it on the cobalts . Only reason i say this is because the rear suspension is a solid straight through rear axle so there for the ride quality is not gonna be as effective as they should be ... most they will do for you is just a drop in which you can get from a decent set.
They are just nice because they are adjustable and if u auto x ur car they are great. of course, if ur not doing this then whatever lol. I would get SSC springs. They are affordable and offer a nice drop but not too much. I had em on my old cobalt.