Unless the intake is outgassed in an oven for several hours and then blasted, any oil / carbon / gunk / old fuel stains / etc. will all return ... except they'll be trapped forever under a layer of clear which is pretty indestructible --
CeraKote is marketed as "the world's strongest clear coat," and they aren't kidding.
Get particulars from the shop you intend to hire on what prep they're going to do and ask questions about warranties and guarantees (if any) if the promises do not match the results, especially over the long term.
I spray CeraKote here too, though I don't use it by itself ever except on buffed / polished metals I restore. The only thing expensive about it is the material itself ... but a little bit goes a LONG WAY. The "tester size" is 4 ounces, costs $35 and has more than enough to coat at least two dozen intake manifolds (you can even pour the leftovers back in the bottle). You can also do it yourself if you have an HVLP gun with a .08 mm tip but I wouldn't recommend it unless you can cook the intake for a few hours first in a dedicated shop oven before blasting it to bring all the leached in gunk to the surface.
Most of my customers are looking for a finish that replicates the look of brand new aluminum but stays that way forever without a lot of upkeep or maintenance. To be clear though, these are NOT "just aluminum" with CeraKote -- they're all powder coated silver first (some with accent colors).
Before (for the Richard Petty Museum
) ...
... and After:
I hope this helps with your decision. If I can help with the job or with any other questions you might have, don't hesitate to get in touch! As a Gold Member you'll enjoy a 5% labor discount but there's others for military / law enforcement / first responder / Liking my FaceBook or Twitter Shop Fan Pages, etc.