I had some cheap quality ebay coilovers once. It turned out that they jack the spring rate up to like 500 lb/in or higher some times. This is what generally cause the horrible ride quality. When I put in my tokico blues it helped some for control but the ride quality was still horrible. The best you could probably do to seriously improve your ride is replace the cheap coilovers. Either with other coilovers (Skunk2, Ground Control, Tein...) or with springs (Neuspeed, HKS, Tokcio...). The spring rates are going to be softer between 200-450 lb/in which gives you better ride quallity and still great handling.
