Strings on vintage guitars
 

I read somewhere that vintage guitars sound good with strings which are well-worn. My fifty-year-old dreadnought seems to respond well to older strings, and sounds too brash and 'metallic' with new strings.
With the older strings some sustain is lost, but the tone seems good for blues and early Dylan material.
Does anyone have any views on this?

Yes and no.

Your dread is a '70s dread? Played in by now I expect.

Some prefer brand new strings and some don't - it's a personal thing. do what suits you best.

Some strings do need a couple of days before they lose their “harshness” and mellow out and or “settle in”. However, I think it’s worth experimenting with different strings until you find the alloy and gauge that marries well with your guitar. If you prefer the more mellow sound, try silk and steel or silk and bronze. See if that mellows out the guitar right off the bat. It’s a relatively cheap experiment.

Strings on vintage guitars
 

Martin Monels: play like new strings (sustain, intonation) but sound like old strings (warm, woody) once broken in and, if you're playing a pre-1960 guitar, period-accurate - very reminiscent of the old New Brunswick black-box Black Diamond strings, but without the neck-/finger-killing tension...

I have a couple vintage guitars where I like old strings but on the bulk of my vintage instruments, I prefer new strings. For me, the sweet spot is about day 3 through about week 2 and then I start wanting to change them but usually hold off until week 4. After about 5-6 weeks, I get annoyed with myself for not changing them if they're still on.

I prefer new strings that have a couple of hours of good playing time on them.

I like what John Pearse Pure Nickel and Martin Retro Monels do for older acoustic guitars. Very full, rounded trebles and mids, pure uncolored tone while maintaining sustain. The John Pearse Pure Nickels are a bargain price too when getting into the nickel metal strings.