Walnut grays over time by itself (becomes ashy).
If you put the veneered piece out in the sun, first of all the heat may de-laminate that veneer, then you have a larger problem.

I would go with what the spouse wants, so much less work and you get the look you want.

Trying to age wood is unpredictable with the outcome, each wood has different ways of aging and showing wear.

Thanks MR. :)

The old piece is the veneered one--it's that perfect shade of mid-century orange that seems so hard to match.

I think the spouse and I have come to a compromise where the spouse has to get all the TV components to go wireless and I don't have to do anything to my old cabinet which supports the TV. So the hutch thingy is no longer needed. A win for everyone! Or at least for me. hehe!

Depending upon how old the piece is (and what you use to finish your new piece), the new piece could catch up in a couple of years. Walnut is one of the few woods that gets lighter over time, more of a golden yellow. In my experience, linseed oil (either straight or as part of an oil-varnish blend, will make the walnut much darker originally. I'm trying to remember the last time I shellacked walnut and can't recall how much darker it made it. It would be worth a test.

If you wanted to go the intermediate route, you could find some butternut (AKA white walnut) and adjust the color to match. Butternut (Juglans cinerea), being in the same family as black walnut (Juglans nigra) has a very similar grain structure. Butternut is softer, but that may not make a lot of difference for your application, as it would for something like a table top subject to much more impact and pressure.