Adding a Film Effect in Final Cut Pro is actually something many have written about in the past.
The Final Cut Pro guide, available at any book store, has always kept a section that they usually title "Video Sex" or something to that effect. In those areas they discuss way's that several other filmmakers have applied a film-like filter set to their film.
In one instance, a filmmaker used two layers of the film. The top layer was only 40 percent opaque, and was de-interlaced and had a flicker filter in the upper field with a gausian blur filter with a 30% blur quality. The primary lower level was left 100% opaque and included a lower-field flicker filter.
Myself, I've found that I like to have the top layer more around 20% or less opaque, it helps to make the image less blury. I do like the 30 percent gausian blur effect, but I tend to go with a flicker-filter MAX setting for both the top and bottom layers as well as de-interlacing the layers.
Overall, there are many ways to achieve this. I really do recommend buying the Final Cut Pro books, it really doesn't matter which version because the point of buying them is not to COPY what others have done, but to take FROM that and mold their ideas to your own style.
Best of luck.