Honda balances their rotating assemblies to 10,000 rpm. i wouldnt worry about the block when raising the rev limit unless your motor has an undersquare rod/stroke ratio.

higher tension valve springs help prevent valve float... when the valve doesnt follow the cam, skipping off the lobe. this can cause valvecrash. it's due to the engine rpm exceeding the limits of the valve springs in use, or the cam lobe profile exceeding the valve springs if you have after market cams.

you want valves to snap back quickly, to follow the cam lobe and prevent valve crash. lightening the valve also helps, in combination with a tighter spring.