Personally, I'd avoid any kind of sealer (like polyurethane, shellac, etc.) on these enclosures. The OEM did not seal them, and as a result it is fairly easy to restore them. A little cleaning and care will continue that for a few more decades. Paste furniture wax can be used as a final protective coat since it can be stripped clean without using aggressive chemicals or mechanical removal (sanding) that may permanently damage the veneer.
If there is no damage to the surface, applying an oil that is compatible with the glues and stain should be safe, and still allows future reconditioning without stripping off any sealers. Any mineral oil based furniture oil should be satisfactory. If the surface is UV bleached, dry, or dirty, the oil will penetrate and CAN even up the color. Even if the surface is dirty from embedded dust, the oil will not prevent successful cleaning in the future to remove the dirt, and may actually help in cleaning. Again, the mineral oil will not interfere with future refinishing efforts. Other types of oils MAY cause problems in the future.
For complete refinishing, a penetrating oil stain made for wiping is best, even if the Peoples' Republik of Kalifornica thinks it is unsafe. Water-based stains and non-wiping stains are great for spraying on in a furniture factory (maybe) where they will eventually be top-coated with a urethane clear and shipped to WalMart, but they're not so great for refinishing. Carver-Tripp oil stains are great for this purpose, and many other reputable manufacturers have similar products, and have for the last century or so.