All valves in internal combustion engines will suffer the fate of carbon and combustion by-product build-up as your photos show. Clean all you like - they will be coated again in a few hundred miles.
Use the appearance of what you have as a guide to engine condition and mixture accuracy - the light brown, dry, hard deposits on exhaust valves are usually indicative of a correct mixture and an oil-tight engine.
Some of your valves (particularly inlets) showed signs of oil ingress making the deposits soft and black. Expect inlet valves to be darker and with hard carbon deposits. Soft and black = oil. If on the back only, then usually valve stem seals are letting oil by. On the face only (usually accompanied by softer oily deposits on the piston tops) indicates oil coming up past the rings.
Fluffy black carbon deposits indicate a rich running engine.
Bit like spark plug reading really...but more informative.
Look carefully at the bevelled face and the matching seat in the head. Black spots show where combustion gas blow-by has started to burn the metal. In extreme cases (particularly on exhaust valves) this can lead to a V-shaped cut in the valve sealing face leading to loss of compression on that cylinder - normally this would have been recognised in the running engine as a misfire, particularly under load, e.g. accelerating up hills. This is not to say that inlets don't burn too - a small defect in the sealing can lead to hot combustion gases leaking back into the inlet plenum past the valve, burning the seat / valve as it roars past.
Any black marks on valve sealing face or seat in the head which cannot be removed by mild engineering , i.e. minor refacing of valve and seat and subsequent lapping-in, indicates that the valve should be replaced, probably along with the seat insert.
Some modern fuels claim to reduce deposition of material on the valve heads and stems due to increased detergent action and efficient complete combustion. Shell V-Power, for example, claims not only to minimise deposit formation, but to do the work that you just spent hours achieving - i.e. the removal of deposits left by less efficient fuels over the years!