I don't know if you should sell it, but a newer bike is worth considering. I had a similar era Miyata 210 (not nearly as nice a bike as the 720!), and I was pretty amazed by how much better the LHT I replaced it with was. The main issue is that those old skinny-tubed bikes get pretty floppy when fully loaded, a modern bike with stiffer tubing handles a lot better with a load. There's also the matter of lower gearing, bigger tires, etc, but it was the improvement in stability that I noticed the most. On the other hand, the 720 will ride much better than an LHT when it's unloaded, so if you just ride it around a lot or tour light, it's going to better for that. Not to mention being a beautiful classic. If I were going to be doing a loaded tour, though... honestly, I would buy an LHT or similar, but I would also keep the 720.