Personally, I'd be fine with driving the car every couple of months through the winter - if the roads are dry and free of salt/mag. chloride/gravel.
Mind you, a quick spin around the block doesn't really work. The important thing is to get all the fluids up to operating temp. for an longish period to get rid of any condensation that may have build up.
I wouldn't consider 30 days without driving a long period either. I have also had unplanned situations where 2 months have gone by and no one has driven one of the Spiders. I don't worry about this any more. If I plan on not driving the cars for a while, then I do mix in the gasoline stabilizer, and pump the tires above what I normally run. As far as the fluids, I make sure that the Spiders are always well maintained, so there is really no need to do anything special. I also try not to leave the fuel tanks low, just as a matter of habit. Things do vary according to climate, and of course you do have to watch out for rubber drying out, and fluids deteriorating when a car sits, but certainly driving once every 30 days is sufficient. As Joe pointed out, driving really means a long drive (or real use), and not just starting the car up in the garage or simply going around the block.
Due to roads being salted all true winter here in Denmark, I don't drive my Spider from November to April. I have it in an underground parking lot which is dry and never below freezing.
Doing this period I remove the plugs, drip some oil in and turn the engine over in intervals for some minutes to circulate the oil round the engine. I do this twice during the period and on the day I take it out to the roads again. Always with power from another battery.
I once a year change the engine oil, always just before driving it to the parking lot (a 15 miles trip) and prep it like Enrique except I have the gas tank brimmed. I change coolant every second year, again just before storage.
Around here, it can get depressing in the winter, so I suguest a drive when conditions permit, salt, ice, snow and such. Just to get a smile back for a while. I have driven my spider on ice and snow and it always has excelent traction and predictability, just dont like salt.