When I got my 75 Formula 400 I started to restore it thinking I should keep it a collectors item. Then I realized after dumping a lot of money into it I wasn't enjoying it. So here are the reasons I decided to go another direction:
1. It was not a collectors favorite year and I had no desire to sell it, show it. I wanted to enjoy it until I was too old to drive it. It was my favorite model muscle car so it was here to stay.
2. Looking at it, I hated the nose so I put a 70 nose on it as it was intended by GM. Now it looked like the Firebird is was supposed to look like. I took off the vinyl roof too because they only look good when you first wash or Armour All them. The rust around the windows was another reason. There is a reason why toy makers only make 70-73 versions. I happen to agree with them.
3. It had a smog motor with single exhaust and cat. Nothing sounds better than dual with headers. The smog stuff had to go. 75 is the cut off for California smog checks
4. There is a lot of potential for the car and it was never going to be realized until I made improvements to it such as handling, power, comfort, sound system, and that meant I can't keep it stock.
5. Finally, I had to make it me...I had to make it mine...like no-one elses, the way I like it when I drive it.
What ever makes you happiest when you get behind the wheel, that's what matters.
I hope this helps.