That Quaid dreamed Melina before going to Rekall is irrelevant. To quote the Rekall spokesman who tries to talk him out of the dream, "She's real because he dreamed her?"
See, you brushed it off just like the film does...but how
does he dream her before he meets her? The options he's given at Rekall are nowhere near specific enough to design her so perfectly. The novelization sneaks in an excuse for this one by having Quaid ask Melina about Rekall. She tells him she used to model for them.
That's one of the problems I have with this movie, it doesn't play with that idea too much even at the end when supposedly the dream will either end or "real life" will continue.
But that's why it's so brilliant! Unlike most films that tackle these kinds of ideas, TR isn't pretentious or precious with it. It's a kick-ass film even if you don't take in the details at all, so it works both ways.
For the record though, if the white-out at the end of the film is to be taken as the "dream" coming to an end, it can't be Quaid waking up. It has to be his lobotomy. (If it's a dream, Dr Edgemar is telling the truth, so we have to take all his dialogue as truth surely?)
P.S. I'm not actually trying to change your mind. I just love arguing the two sides of the film. Six months from now, I'd probably advocate the "None of it really happened." approach.