I agree that in both novels there is an idealized love object: in the one case, Estella; in the other, Daisy. However, the overall frameworks of plot and themes surrounding the love interest are quite different in the two books.
In Great Expectations, unforeseen wealth elevates Pip to a...
position in which he can continue to obsess over Estella realistically, as he sees it. When he finds out his status is the gift of the convict Magwich, Pip is horrified. As George Orwell wrote,Great Expectations is largely a novel about snobbery, a destructive kind of demeaning attitude that persists even in the modern world with our intended egalitarianism. In The Great Gatsby, Gatsby's wealth—which supposedly will enable him to win Daisy—is not a gift but self-earned, though by means not on the up-and-up. Gatsby's association with mobsters parallels Pip's connection with Magwich but is a deliberate association, not one occurring by accident or by fate.
It would be a bit simplistic to say that Gatsby represents the modern world of the self-made man and Pip the old world of inherited wealth. The more important point, made by both Dickens and Fitzgerald, is that wealth in itself is a kind of illusion, just as both Pip and Gatsby cherish an illusion in their idealized love interests. In each situation, the love interest is false in some way, though in the case of Estella, we have the sadly neurotic intent of Miss Havisham pulling the strings, creating and manipulating Pip's fixation and leading him on. In Gatsby, there is no such external device that has triggered his love for Daisy. Instead, the recurring motif in Fitzgerald's work of a man viewing a woman as a goddess of sorts is an analogue to the wider illusion of wealth and "success". With both Dickens and Fitzgerald, however, the underlying idea is the same: the transience of happiness, whether from material gain or not.