To follow up, I mentioned my conundrum to a relative, and he referred me to a high school buddy of his who practices law in Oregon.
His primary focus is real eatate law, but he's also an avid rider (told me he has over 35 bikes in his collection, and rides over 30K miles per year), so he also takes cases involving motorcycles.
He told me the statute of limitations in Oregon is 2 years, and to just wait and see how my shoulder is doing after some time, before I even consider settling. He also said their offer was well below average, but every case is different. He said when I think I'm ready, if they give me any trouble, call him. Also, he said don't sign anything (obviously), especially anything giving them access to my doctor or my medical records (first pile of forms they sent me, which I didn't sign or return).
This was all done with a free consultation over the phone, which he does for anyone. So if anyone in Oregon has the misfortune of needing an attorney to represent them in a personal injury case involving a motorcycle, PM me and I'll forward you his contact info.
Since I'm still experiencing daily discomfort with my shoulder, I returned their check, and told them I'm going to wait a while longer to see how it goes.