I'm sorry you and Buddy are going through this, rustybucket!
We had a springer (age 6) that had an arthritic spine. Between getting both her hips replaced due to dysplasia, we found that her back was causing her a lot of pain and the pressure on the nerves was causing her to lose function in her legs. So we had a surgery done that sliced off the top of the vetebrae to enable the surgeon to carefully remove some of the material that was pressing on the nerves. She died just before her 15th birthday of unrelated causes and her back caused her no more trouble in those 9 years post-surgery. Even if she'd been 10 at the time of diagnosis, we still would have given her another 5 pain-free and functional years. So Buddy's age may not be that much of a factor, and there are things that can be fixed surgically or otherwise.
Proper diagnosis and info on prognoses with and without surgery may help you decide, and it might not involve an MRI. Given what we've experienced with our dogs past and present, if it were us, we'd likely find a good veterinary orthopedic surgeon and have an evaluation done. We've had very good luck at the local teaching hospitals. Orthopedics specialists treat many more cases like this than regular vets see and often can suggest therapies other than surgery. They often see things in xrays that our regular vets miss entirely. It might at least be worth a consultation for Buddy.
