I would flat it off and have a go prime and paint, trouble with plastic if you take him down to the plastic you will need plastic prima etc so I would flat him carefully and paint ontop.
sounds like you have done some reserch in to it , so you will probally know about paint reactions, I painted a boot spoiler for er in doors coupe, bought from
, what a mess, it had about 3 colours on it, I took it down to much and exposed the origonal yellow colour, no worries, grey prima filla fine, red prima on top, fine, finished in Capsicum red + laqure, excellent, bolted to car within a week bubbles? more and more.
Paint shop told me it is air in the fiber glass, so they baked it to make the air expand , once this had happend they primed it with plastic prima but it went even worse. always on the yellow paint though, so they said skip it and get another, well not to be beaten by a lump of plastic, I sanded the whole spoiler down to the fiber glass, and did the same prima filla, red prima, topcoat and laqure - fine, no bubbles, no reactions so what I am trying to say is it is not always straight forward, all the other layeres of paint on my spoiler where fine, it was the yellow paint layer which caused all the problems, which was the origonal Renault colour.
I am sure you also know that if you are spraying metallic paint it is very difficult to match colour, shades will differ due to paint mix, spary gun presure, drying temp, and depth of coats.
I would be tempted as well to give it a go, bodyshops are SO expensive these days, one of the things they did tell me was palstic is better air dried thank oven baked, less change of paint bubbles.
Remember if it does not get a good finish, another old sprayshop trick, get your old wet/dry (12000 grade) and flat off the lacquer very carefully don't go through it just take the top off so it is dull (careful on the edges/raised ridges(thinner paint)), loads of water, very gental rubbing, loads of concentration.... then using a cutting compound buff it up, again careful on edges and ridges, then polish it comes up like glass, leave it a week 1st though to completly harden, thin finish on my spoiler is better than the car, we use to do this when we painted herses 4 coats of black paint flatted after each, then 3 coats lacqure flatted after each, then final wet coat, allowed to harden then flatted and buffed, what a finish!!!! undertakes would come from miles with the cars.