Ouch, I practically grew up on FF. It's such an ICONIC cover....how can you not want a copy for that reason alone?
Wen I started reading/collecting comics in 1987 as a kid and Marvel fanboy it was Uncanny X-men and ASM first, followed by GI Joe and Transformers. The FF was a. Third tier title by then......just like today........If I wanted a Marvel SA key outside of AF 15 now it would be a Hulk 1 or X-Men 1, not a lowly FF 1.
Besides, why buy the knock off (FF 1) when you can get the original, BB 28, instead?
If you're looking at it as a collector, your point of view makes more sense. As a reader, FF 1-102 beats the first 102 JLA appearances.