Hi Dave,
Yes - there are benefits and - No - they are not just cosmetic - some companies can supply black ones if you prefer.
They last much longer - that's about it - they don't 'sweat' like my original ones did - and they are a good bit stiffer so don't collapse or blow up / expand. My old ones wept oil from the joints - no matter how tight I made the Jubilee clips.
You need to have good hose-clamps - use the 12mm ones not the skinny 9mm ones. After so much tightening with the old hoses I renewed them all.
The most troublesome joint is the 90degree one where it enters the EGR - I fitted a 'T'-Bolt clamp there.
I also fitted a corrugated type silicone hose for the air intake too - that was a little bit of cosmetic - so the whole lot look pretty good now.
Derby Performance Hoses are a small company who will also make up 'one-offs' - they do a lot of classic and veteran car hoses. Very nice people - personal service when I visited their little industrial unit last year.
DPH hoses are 5mm thick - there are some 4mm or even 3mm ones on eBay.
Singvogel.