My male piggy often has quite a 'stinky' smell about him.

Everything I have read on this subject advises that this smell will reduce after neutering but will not completely go away, some regular grooming should help keep on top of it ! Could be that his grease gland needs a clean !

The males have sacks by their genitals, which, since they walk so low to the ground, collect poos, bedding and dust. The longer the sack goes unemptied, the more it smells. The smell is stronger if wood bedding is used, as it mixes with the poos, and doubles the odor. Check the sack, and if necessary, use a cleanex or paper towel to gently squeeze the contents out of the sack. I good moist wipe of the area helps pick up any stray junk, and neutralize any remaining odors.

That's a good idea, I truely would not recommend neutering the cavy. They are very stressful and they are not good at environmental changes. So, your method will work at the best potential.