Those light color spots on shelves would concern me far less than the fact you can't smell your plumber. Never seen one yet that was any count useless he has tobacco drool and stinks.

Those light spots is where varnish finish has worn off exposing raw wood. Rough finish is simply result of abrasion from sliding things across wood. Whip shelves clean then slap on a coat of shellac followed by a coat of polyurethane varnish for another 20 years of protection.

You might want to buy some stick on floor tiles and put them on the floor under your sink. It looks nicer, and cleaner, and its much easier to wipe off. You could use vinyl flooring too, but, I find its easier to cut tiles, around the pipes, etc, since my pipes come up out of the floor.

The dark spot was probably caused by something oily. The 'wood' looks like particle board or some kind of fiber board and the bumpy texture is just what happens with those sort of materials over time and with humidity like you would have inside an under the sink cabinet.

I would do as Cat suggests. Or buy an 'undersink mat'.