On hire karts wire and tear is pretty easy going, there is a reason them things weigh so much compared to there racing counter parts

.
Those Honda engines will run forever in a day so no need to worry much about them. Usually hire karts have (forgot the name of the material) special toe rods on the front that will just absorb the impact and spring back to shape. Maybe chains would be the part most often changed, but again usually hire karts have pretty heavy duty chains and are just run till they break.
Only thing I'm not hugely sure of is clutches as you often get the people who seem to press both pedals at the same time. Can still smell the burning from my local kart tracks open day last year where they gave free shots of the pro-karts
A local indoor karting place near us, they have just moved to a new place and they've laid this very grippy surface which they are regretting. They are just chewing tyres up compared to their old painted tarmac floor.