We own a 95 855 and 98 S70 T5M. The power train changes were minor.
The body was smoothed and the windshield raked back a bit. The
wheel wells made larger, etc. I use many common service parts
between our cars (oil filters, air filters, etc.). Interior changes
and suspension changes are what most people would notice.

Safety changes included slightly better knee bolster; improved side
impact protection (B pillers are stronger) and the steering linkage
was completly redesigned (crushes easier when your chest hits it)
for the 70 series.

Bigger changes started in 99 when they introduced electronic
throttle; 5 speed automatics and variable valve timing and side
air bags that included head protection, different oil fitlers, etc.
So, under the hood changes in 98 were minor.

The 70 is basically a mid-lfe kicker for the platform and I'd call
it an evolved 850; not a revolutionary change.