You will have to change the springs if you go to plain shocks. The nitrogen cells provide considerable spring, too.
I'd look around for a set of used struts -- they usually only go bad if the accumlators go "flat" and the car is driven too long with the rear suspension locked up from no strut travel. I lucked out, the ones on my TE weren't bad when I got it.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!