First of all, you must understand that Spice, like spectre and Eldo and others are simulators not models.., the models are suited to work with the simulator, for example the most famous model for integrated MOS transistor is BSIM3, so you will find BSIM3 models for Spectre, for Spice and so on.
The model is provided not only for parasitics, it also defines the performance of the device itself,
The design flow for Ic design is 1. Device charactarization 2. schematic design 3. Layout design 4. DRC "Design rule check" 5. LVS "Layout versus schematic and finally 6. Post layout simulation.