The last time we went over springs was quite a while ago, I don't know where it'd be either lol - the modifications list is a nice thing to run through regardless (
http://micra-forum.com/showthread.ph...mizations-list )
In regards to just lowering the car - N15 put together a list of aftermarket springs for the car so you can compare the spring rates they have to get an idea.
http://micra-forum.com/showthread.ph...-for-k13-micra
When I did my calculations (putting a known weight in the driver and passenger seats - measuring the change in wheel gap), I found that 30% of the weight added to the front seats is transferred to the front wheels, with the other 70% being sent to the rear (rear seat ballast is 90-95% on the rear tires). Stock front's seem to be around 2K (110 pound), and 2.5-3K (140-170lbs) in the rear - So you can likely get away with a 2.5K in the front, and a 3.5-4K in the rear and be fine...ish. The rear springs are what you'll notice most though, and I'm not solid on what the stock shocks can handle in rebound. Nobuseri (another owner on here) has used a progressive spring from RS-R (a "Ti2000" but I don't know which model exactly), thing sits beautifully but I don't know what the ride's like.
I went the coilover route and have 2.5K in the front (would like 3-3.5K) and 10.5K in the rear (used to have 15K but the rear end was going airborne), it's bumpy but fun