Picked up a set of spring H&R springs that fit a 2005 to a 2010 Scion TC...
Then doing some Googling I see that a TC weighs about 2904 lbs.
My 1997 Jetta weighs approx 2725 per the same Googling...
I wonder if the spring diameters would allow these to fit...
179 lbs difference...
I would check the spring rates. Maybe get a hold of H&R. Suspension design has something to do with spring rate too. But the worst that would happen is a E36 M3ty ride i think.
Springs rates near enough are spring rates... but wheel rates are also wheel rates. With the right leverage you can use pretty much whatever spring rate you want to get whatever stiffness at the wheel you want (though it may not make sense to do so...)
I guess the biggest problems are spring length and coil size.. if the springs physically fit.. then I guess it can't hurt to try