Absolutely no guilt buying new, support the industry and the world economy.
However, if you can manage the Holdsworth frame size, few upgrades are needed.
Get fatter tires, new brake pads, shorter/taller stem - those things you can do easily.
You can reach downtube shifters, but barends and brifters make it easier and aren't much work at a shop that serves used bike customers.

There's also no sin in an old road bike upgraded AND a new bike. Having a back-up bike or fendered rainy day bike or errand runner with racks or hardcore gravel traveler - never hurt anyone.

Life is good.
Ride on!

edit: seeing your Holdsworth, you know it's a keeper. Stem + bar swap. As others stated stems can be tall; new handlebars also come in 'short and shallow' to stay with drop bars.