While cleaning up my front arches over the weekend I noticed the bottom bushes on the dampers are pretty shot. could twist the damper with my fingers.

Are these replaceable parts or do they come moulded into the dampers?

I noticed they are different from the earlier 300 style with a bar going through the bush with a bolt on top, much easier than the one bottom bolt setup.

The disco drives ok, not perfect but ok and apart from worn front anti roll bar bushes i'm going to replace today, everything else is good.

Will i see a little improvement by changing the front dampers?

You've posted under Disco2 modell albeit from your signature seems that you have some late 300Tdi, anyway afaik the D1 doesnt have such bushes so if it's D2 here's your answer www.discovery2.co.uk / Workshop :- Front Damper lower Bushes

It's a Td5. Cheers.