A little TJ here (sorry Jo ) But after workin' mine over with the sander, I had no problem feathering/blending in the hood scoop & fang extender thingies using a strand reenforced bondo (kitty hair). That was over a year ago, & so far no problem.
Where I have had problems, is with moisture bubbling up under the finish. It's like the bottom side isn't sealed well enough, & allows condensation to infiltrate up throught the panel...
Another issue I had, was my own lack of forsight, I applied the hood scoop & fang thingies with 3M double stick, & mistakenly thought that the bondo would also act as an adhesive...wrong! Cracked all the way around the perimeter of all 3 peices.
When I get around to a "do-over" I'll use a high quality epoxy, like PC-3 or equivalent to bond the decorations to the insert.