True... quality coilovers aren't cheap, and I don't advise just throwing together a crappy coilover setup. You're just asking for trouble.
Not necessarily. You could easily match the stock spring rate with a really soft spring and the ride would likely be BETTER than stock. In fact, my coilovers have nearly triple the stock wheel rate and the ride is very liveable compared to stock. This is possible because coilovers correct the poor stock spring geometry and significantly lower the total weight of the spring/damper setup.