My 2 cents:
I read (and believe),unless the seat is a good(shaped) fit for you,the gel wont make much of a difference.(At least I do believe that for my seat!)As far as just adding the gel pad on top.
I think that's why some people like the gel,some dont.It depends on if the seat was a pretty good fit to start with.
Of course,you can try your gel seat and maybe prove this wrong.
Although I think it all depends on each person and their behind,they're all different