Barefoot is definitely not the answer for all navicular horses. I may very well help some, but depending on exactly what is going on and how advanced the syndrome is, barefoot can actually be quite harmful. Every horse is an individual, and if your vet and farrier are experienced in this regard, I would trust their judgment (with the caveat that not all vets and farriers ARE qualified, and it's best to look at their track record in treating similar horses as well as their general experience, knowledge, and openness to trying new things if the current protocol is not working). Are they having you put any kind of cushioning pad underneath the bar shoe? That may or may not help, but again, they've seen and know the horse.
I would also caution you against jumping, unless you have the vet's 100% approval (and s/he is not of the mindset that "horses are for using, so use them up," as many vets are). Since your horse requiries maintenance to maintain an adequate level of soundness, I would really think that concussive riding force like this may not be the best idea.
Bute, giving a gram or two a day long term, is definitely not ideal, but it's also unlikely to all that harmful, particularly with an aged horse. Weigh the costs and benefits. Many horses are on daily bute, and live that way for years.
Other options to look at, should the necessity arise, are joint supplements, coffin bone injections, navicular bursa injections, Adequan/Legend, or Tildren.