There are several of us on this forum that have had joint replacements. As I recall from previous threads on this subject all of us that put them off pretty much wished we'd done it sooner. I can certainly say that holds true for me in my full hip replacement.
I assume by "doc" you are referring to an orthopedic surgeon and not just a general practice MD? You also might want to get a second opinion. I do know that joint replacement (don't tell your wife, but it's referred to as an implant.

) has came a long, long way since I got my full hip replacement in 2005.
While I felt the pain from the surgery, I knew as soon as I came to that the pain from the hip itself was gone. Eight years later, I still don't have much issues with it. I'm not able to run like I did before the hip problem (a result of a motorcycle accident a year and a half earlier) but every thing else is pretty much back to normal. I can feel it going up and down stairs and hear it making noise but it's not painful.
Back then, the knee replacement had a longer recovery time but I think that's decreased for knees since 05. I'm sure others will lean in here and share their experience.