Any protection is better than none.
I use roller blade knee-cups that I bought at a sporting goods store. Very sturdy and thick plastic cups, comfortable, cost about $10 on sale, been using them for years. Just as good or better than the $25 - $50 motorcycle ones. You do want some sort of plastic cup over your knee cap, not just a pad, IMO.
Many people don't wear elbow & forearm pads because they are can be uncomfortable or hard to get used to, but at $5 it's worth a try.
If it makes you feel better, many of the riders in the '70's used chest and mouth protectors made by Jofa, a European hockey equipment maker.