If I go down the hydraulic disc route it also means new shifters as currently he has brake and shifter units combined, also need to buy rotors on top for both shimano and avids as he has centrelock hubs, the M495 are £32 each end complete with centrelock rotors and have a pretty good write up when reviewed on Bikeradar.
The advice above re setting the V's up properly, I have them set as close to the rim as is possible while still allowing you to unclip the noodle for puncture repair, can't see any flex when I apply the brakes, levers are as close to the bars as feasible and as far inboard as poss to allow max leverage, pads hit the rim nice and square, cables nice and clean, only 6 months old, rims spotless, pivots nice and clean and lubricated, no sticking arms or anything.