I'm 65 and continue to ride vintage road bikes with drop handlebars, including my Ron Cooper that I bought new in 1981 and my grey and yellow Miyata which is identical (even the color) to [MENTION=244722]Cougrrcj[/MENTION] 's Miyata 710 pictured above. I've made substantial adjustments (gearing, bar/stem position) to match my age/condition and the epic hills we have around here but am just as happy with the bikes as I've ever been. I briefly went with a newer Trek but sold it because it was less pleasant to ride than my older bikes.

That Holdsworth is a beauty. I would strongly suggest that you make a few adjustments to the Holdsworth. For someone who is not racing, the difference in riding characteristics between a high quality vintage bike and a new bike is going to be negligible unless you live in a hilly enough area that the gear range is insufficient. Barring issues with gearing, I'd start with a shorter, perhaps taller, stem such as a Nitto...they make several different versions of the Technomic which vary in height. Barcons would also be helpful. As to switching out the handlebars, that is personal preference. Personally, I like drop bars because I can ride the tops, the corners, the hoods and the drops. In comparison, most other bar types have very limited hand positions. I think the important thing is getting the bars to where you want them using appropriate stem adjustments.

P.S. In case you don't take this advice, I'd be happy to pay the cost of shipping and then find a suitable location to dispose of that old piece of junk so that you wouldn't have to deal with it any more.