Repainting my front spoiler - Steps?

[Kepico]

Apologize if this is in the wrong section & I know this may be a bit more than 'detailing' but I'm figuring most in this forum would have some paint experience as well?

Here's my situation; I have a 1988 Conquest\Starion (Mitsubishi), the lower portion of the front spoiler has seen better days (paint chipped off etc. probably from hitting parking curbs etc back in the 90's I'm assuming). I ordered up the correct touch-up color (Rio\Mexican Red - R04) but upon applying it I've noticed it doesn't really match the rest of the lower spoiler color. I don't think it is from OEM paint fading as normal (the rest of the car is original paint and has faded a bit normally but this seems a bit darker than the rest) I believe at some point early in it's life the spoiler was re-painted and is 'slightly off' in color (the current paint on it is fine, just mis-colored).

Figure I have 2 options;

Somehow\someway match up this current color?

Or go ahead and paint the entire lower spoiler the one correct color (R04\Rio Red).

I have found a variety of things on the net regarding the repaint and had few questions to make sure I got the steps right?

I believe it would be; scuff\sand the current paint slightly - apply adhesion promoter (plastic) - color coat - clear

I'm a bit confused about the adhesion promoter & primer. Do I need to put down any primer anywhere in those steps or does the promoter replace the primer? My current paint is fine (not bare) so I didn't think I need a primer at all?

Thanks for any help!