Let's see pics of it!!!
Clean them up and scrub well. Clear coat things that aren't high-heat. Re-paint anything that has gotten dull, just back to black or silver. If your rules do allow some color and you like it, maybe some "Ford Blue" on some parts. They make that in engine paint so you can do some high-heat parts, too.
I do this on my cars as I am working on things. I take off small parts, hardware, etc. that are worn looking and do this on the side while I replace the radiator, etc.
Here is a car I'm cleaning up now. This is a 00 Volvo turbo wagon. As a joke to myself I paint parts I modify "Swedish Racing Green," (joke name for their traditional racing color - basically Ford Blue). It's all invisible with the hood down. A simple thing I did that was surprisingly quick and effective was spray foaming degreaser on the cast intake header, scrub it after 5 minutes with a little wire brush. Gleams now, nothing else. I'm going to thoroughly do the visible head parts next time I'm messing around in the engine bay.
Besides scrubbing cast parts, another "bling" thing is to clean and coat the black plastic. I wipe them down with a ~60/40 mix of boiled linseed oil and mineral spirits (same as I use on exterior plastic/body cladding). You have to let it sit and cure but then it provides a very long lasting "like new" appearance to the plastic. Resistant to lint and dirt once cured - unlike lots of plastic dressing.
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Small hardware that gets bad I refinish, simple process of wire wheel on the bench grinder, de-grease, let dry, prime and paint. Takes a few minutes each step and makes a nice little break between steps in bigger projects. I did this PS hose bracket in the Swedish blue, but could do it in the black of course to not make it stand out so much (did that on my step-son's S60).
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There's a interesting video from "Chris Fixx" on engine bay clean up, sounds like you don't need it but it's worth viewing if you haven't seen it. I do have to 2nd his opinion about those vertical-handled brushes. My dad had some in his shop and they really simplify detail cleaning. like this is what I mean:
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CF video:
None of what I do above is designed to be "show quality" but it could be by just being more thorough.