my .02
I guess it's a matter of preference as well as if you have health insurance or not. Last season I had no health insurance, I wore more than probably necessary. I think for some, knees and elbows are worthwhile. As stated above packing the pads on the way up to wear on the way down.
Last season we were at Brianhead and three of our party rode Blowhard sweet ride if you haven't done it. If you know the trail as you come out of the more technical upper section, just before the gate you have some high speed corners in a gently decending open field, one of our party washed her front wheel and clipped her pedal, I was the trailer of the group. She hit harder than I have ever seen anyone hit before in person, a wicked elbow strike. I think that the elbow pads really saved us from a long walk out or a really expensive extraction. Granted Blowhard is not your average XC ride but the section that she wrecked in could have been "anytrail, U.S.A.". I'll probably get flamed for finding the bad in biking but I prefer to ride than not, so yeah to answer your question bring the pads use them if you want it could save your ass. Sorry about the rant the doc still won't let me ride after my surgery, 5 weeks!!!:madman: