An ST-3 is slightly more expensive to insure than a ST-2 on some occasions - no idea why. The ST-3 is a 4 seater rather than 5 so not sure if that is why?
I bought my ST when I turned 21 - treat for me coming out of my apprenticeship.
Personally I prefer the ST-2 over the ST-3 as I prefer the cloth seats.
Interiors on the 07 onwards cars on better on the pre facelifts - nicer centre console shape and come with black headlights and red illumination inside instead of the horrid green.
The ST-3 comes with footwell lights but these are also present on the ST-2 - just without the bulbs fitted. Pair of 501 bulbs and push them into the holders and job done
Rob