I have splatter marks that wont come out on my hood louvers. Looks like acid bird **** (if that exists lol). I want to repaint them what are your thoughts on color. Flat/semi gloss/or gloss black? Id like it to match closely to the stock headlight inserts

Just do the stock paint color. If you were to replace them and custom make your own fully functional hood louvers then you could paint them gloss black. That is the only way I would paint louvers gloss. I am just not sure about gloss on plastic although it doesnt turn out too bad on my model cars the flat looks really good as well though.

So I would say either a flat or possibly semi-gloss.

I was leaning towards flat, thats what stock looks like to me