From your description, those sound a lot like the originals, though it is possible they were replaced by a dealer with Volvo parts at some point before you got the car. One way to tell if this has been done is the presence or absence of undercoating overspray. Original shocks are dark blue, made by Boge, and the flexible plastic upper part is normal.

In any case, it looks like they are way overdue for replacement. If the rear shocks have never been changed, it is highly unlikely that the front struts have either, so, to do it right, you should do them as well. I have had good results with KYB GR2s, at about $50 a corner, but with the condition yours are in, ANY new replacements will make a huge difference in ride and handling.