Mineral spirits might or might not work, depending on what clearcoat was used 20 years ago.It might dissolve or gum up what's left of the finish though. If soap and water won't do the main dirt removal, then the finish is too deteriorated for anything but refinishing.

My go-to is ALWAYS 409 cleaner. It is not a powder, so is not abrasive. I wouldn't buy the newest kinds, like the ones with bleach or germ killer, but would buy the 'old-fashioned' original in the white bottle with the purple label. It is gentle, yet exceptionally good at getting grease, off, which is what will probably be the hardest with kitchen cabinets. IF the finish is down to the wood, anything you use could possibly stain or darken it, so be careful. I also wouldn't use more than a micro-fiber cloth or paper towels. Using a scrubby of any kind is liable to remove more of the finish. When you go to refinish them, use a very, very light steel wool to smooth the finish out and then redo the entire cabinet. You won't be able to 'spot' finish and have them look good. hope this helps.

Thanks to you both. It does seem like a delicate job and I'm not looking forward to it. I wish they put better finishes on kitchen cabinets so they would stand up better to wear and tear.

how about Murphy's oil soap, simple green, bona for cabinets??

i have new cabs and use the Bona for cabs with a microfiber cloth and works well,,,,
20 y/o cabs, i think i would start with murphy's oil...

good luck

Even i was facing problems for the cleaning of my metal cabinets. So in my past search across the search engines i came across i came across so methods like by using bleaching powder and thinners might be helpful as a cleaning agent.