Hi, 3304hl. Much of what you mentioned is known to the Aerodynamics forum. Yes, actual raindrops grow larger as they fall, turning from round to oblong until they grow to an unsustainable size, turn to a parachute shape, and break apart. But an ideal streamlined body looks a lot like half of a cartoon teardrop.
Here's a thread where I learned a lot about diffuser design:
http://ecomodder.com/forum/showthrea...ion-13230.html
If you're planning on sticking around, you should introduce yourself and your cars:
Introductions - Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com