If you like your mower and want to continue to do so I can offer a few reasons why you should treat the physical appearance with the same concerns as the mechanical:
and care for the outside and under your deck will extend the use of your machine by years.
*Washing and putting away your machine between mowing sessions will keep it clean looking but often, that's not enough. A good wipe down with a neutral solvent like Denatured Alcohol will leave the mower stripped of any contaminates and allow you to apply gentle abrasive polish to take away your scratches and discoloration. A final, good quality automotive finishing wax will bring back the original luster...and protect it for many weeks during operation.
*Routine polishing and waxing
will keep a higher residual value of your machine (at top dollar) in the event you'd like to sell, trade, barter or trade in for money or to upgrade to another machine.
If the physical appearance of your current mower is too far gone and the scratches and blemishes are too deep, then it's time to consider a disassembly
, and the process of filling, sanding, priming and painting the machine. I would recommend a good, heat and fuel resistant paint if you're going to use 'rattle cans' or a mid line acrylic enamel if you have a compressor and spray gun.
Hope this helps.