Couldn't care less about opening hood and doors or anything, I'd much rather see my windscreen getting progressively dirtier when racing up close to another car, or as a result of dust etc thrown up by other drivers. Therefore, I want functional windscreen wipers, not just any old rubbish mind, I also want to be able to squirt windscreen washer fluid too. If the screen is REALLY dirty, and you don't use the fluid, should make a suitably nasty mess, so that if you're leading, you can help extend the lead knowing that the further back a driver is, the more nonsense he has to think about in order just to stay on the track.
Of course, being a sim, there are other factors to consider with this addition. Firstly, there would need to be a separate setup screen, which allows you to select the balance between water and washer fluid, how much fluid you're going to use (heaven forbid you should make the car unbalanced with 5 pints of fluid when you could be more conservative with the switch and get away with 2). There'd need to be a closeup view of the windscreen washer nozzles themselves, and with the aid of a small modeled pin and some dexterous mousing, the user is able to set each of the nozzles to the desired pitch so that the screen can be cleared as the user prefers.
Secondly, accurate modeling of the water jets from the nozzles is paramount, because some of us might not care too much about clearing our windscreens too often, but would like the ability to send the jets straight over the roof to totally screw up the view of the messy windscreened git behind you who is driving unsafely close to your bumper.
If this isn't possible, I would like a nice day/night transition, where timescale is set by the server, including time of day/night at which you start. Some weather would be nice too, again with options for changeability.