At some point all of our manifolds will do that. I have searched for gold wrinkle finish paint to no avail. But I did find this, Aluminum Gold Wrinkle | All Powder Paints®
If you try it, please let us know how it works. I've got refinish intake on my to-do list.
Even if you aren't able to easily re-paint the valve cover, you can certainly clean up the rest of the engine bay. You can begin by shielding with plastic bags the alternator and other vulnerable components, and then continue by hosing the engine down with a constant stream of water. Next, spray degreaser—any brand, and diluted to your liking—over the valve covers + intake manifold, etc. Let things sit for a couple minutes, and then go in with a medium-soft brush and agitate the dirty surfaces. Finally, rinse the engine bay down for a final time. At this point, you can wipe the surfaces dry and/or let them air dry. Alternatively, you can use either an electric leaf blower, or compressed air, to accelerate the drying process. Make sure the bay (particularly the alternator) is as dry as possible, before you star the car. Once you do start the car, let it sit a bit and warm up. Residual water will evaporate.
Everyone has his own process for cleaning and engine bay, but this is more or less what it entails. I'm sure it will look great afterwards.