I've heard of people using the "Yellow Box" to correct their speedo. I'm wondering if anyone has used or heard of the "SpeedoHealer"? According to their site:
"Fits ALL cars with 3-wire speed sensor and with 2-wire ground switch sensor"

http://www.speedohealer.com/eng/intro.htm

I'm trying to figure out if this would work on our Grand Vitaras as it's a little bit cheaper, has finer grained adjustability, and there is a Canadian distributor.

The wiring diagram shows a single wire, blue/yellow stripe, between VSS and speedometer.  So it sounds like Case 2.

Only one way to find out 

Btw, I have found out that my speedo reads 5mph fast at 70 mph on stock tires.  So if you fit tires with 6.66% larger diameter, you would be spot-on!