I bought my 67 convertible in 1997 with the spoiler. It was (and still is) in great condition.
I didn't know too much Firebird history back then other than that I wanted one since Hotwheels came out with one in the late 60s (1968 Custom Firebird). It had the spoiler on it. So mine fit the bill of what I was looking for when it came up for sale.
I like mine with the spoiler, but should I want to go back to original, I have the original parts to do it for the next owner that I may sell it to.
Point is, every owner has their own vision of what they want their car to look like. If it's originality or custom, that great. As long as then don't make it look like that stupid Vegas Camaro (posted on this site somewhere), put a massive home made hood scoop on it (also posted on this site somewhere), or God forbid they put a Chevy or Ford motor in it........
1967 Firebird 400 Convertible - White with Bright Blue Interior - Power windows, top and steering.