Call me confused, but it ain't spring failure causing bounce.

Add me to Bob's confusion list.  If it isn't as good as it was when new,
then put new parts back on, like shocks, to start.  Why throw it all away to
go with expensive coil over shocks?

Have you ever worked with a coil over suspension?  It isn't simply taking
off stock shocks and springs and putting on coil over shocks.  The shock
mounts are not designed for the spring loads and you will find you have to
do a lot of design work to get the right combination.

Besides, the fiberglass transverse spring is a good set up.  The fiberglass
spring reacts faster than a metal spring due to less mass (remember
inertia?) and so the shocks can be tuned to the load of the wheel and not
the mass of the spring.

Yea I wouldn't do it either, unless you were going Autocrossing,
and then I check the class rules. You might get stuck with the Big Boys :-)

To just refresh your ride, I'd look into all the factory components and
replace
what was necessary with new factory style stuff...

I replaced my Bilsteins at 95,000 on my C4 with Mid America custom valved
shocks. And it helped the ride, not drastically, but definitely helped...

Unless you are seeing a LOT of seepage on the shocks, they probably
not NECESSARY to replace. On gas charged Bilsteins a little seepage
is normal. But having said that excessive bounce is DIRECTLY related
to shocks, and not springs. Unless you have a cracked spring.