The valves could well have a more pleasing sound, but that is a personal taste. What detracts from valves in my mind is the bass weight and upkeep costs.
Re speakers, I've never heard B&Ws sound good with LINN gear - they just don't seem to like each other. When looking at Ninkas, which I have, the upgraded bases are a MUST! The clarity and bass drive increases are rather stunning.
Another option, which I am currently interested in, are ATC. In a smaller room, I would take ATC SCM7s over Ninkas in a heart-beat. Mine is a bit larger, so I currently lust for 12s. LINN and ATC pair like a Yaluma Shiraz and well marbled steak - simply perfect!
Cheers,
Kevin