Well, if you want better parts you can get some from www.domesticperformance.com
You could probably get the shocks from someplace like www.gmpartsdirect.com
for alot less than you would pay at the dealer. I did a quick check and they look to be between $75 and $125 a piece for the rear struts.
I'm not sure how mechanically inclined you are but I helped my buddy do his rear spring on his Grand Prix and it was extremely easy to do. With some basic tools and a little time on the weekend it might be worth a shot.
As far as 63K miles on them, yea, they shold last 100-120K at least before they start to go.