Here is some idea's for you that I sure everyone has already thought of. Our decklid is Branda. We had no choice but to buy a new one because we did not have one to begin with. After much sanding and adjusting, we got our decklid to fit pretty well (very well before we installed the decklid seal which made it alittle high on back).
Anyway, there are adjustments. I would assume most of you had already tried this but just in case. If you want to pull the decklid down towards the front of the car, you adjust the hinge bolts on the car side. Loosen and push the decklid down in small increments. If you want adjust side to side (to close a gap at the back of the car with the end caps) you would loosen the hinge bolts ont the decklid. Again, small increments.
If you want to pull the back of the decklid down (pulling down the spoiler), you would adjust the latch on the car. Loosen and push down on the car side latch. You will know if you went to far when the decklid won't close. I have done this before and need to do it again now that my seal is getting some age to it.
Lastly, you can adjust the end caps. The bolts are located inside the trunk and you can loosen and pull up just a hair to make the decklid align with the end caps. Before I went there, I would adjust my decklid latch until no more adjustment could be made.
If you have a warpage problem, well then you are stuck with it. In my opinion, I do think the decklid looks better when it aligns with everything else but I also know that many of ours fit better than they did when they were new.
I would not ever change out an original for an aftermarket. However, ours did not turn out to bad.
Hope this helps someone.
Paul