I liked the nod as well that there is more to Fry's delta brain waves than what the Nebulians had.
Of course there's more to it... that lack of a Delta Brain Wave also killed the Brain Slug that tried to feed on him... lol
I liked the film, but I might be in the minority when I say this was probably my least favorite of them... and for a surprising reason, I found... Seeing the gags and characters getting trotted out again, to be honest, I thought things were getting a bit... tired. That made me really excited when I saw the ending and realized that, maybe the creators felt the same thing, as there were several steps taken this time out that can't be easily taken back in a series this continuity-conscious. Relationship dynamics with several characters changed drastically (Amy, Nixon, Kif, Zap, Fry, and Leela were the biggest ones I could think of) which will have to be acknowledged and not swept under the rug in whatever comes next.
And I hope whatever comes next does in fact happen to be a new setting, as I think 3000's Earth and its cast of characters has become a bit too stale, and maybe has said all its going to say... at least for now. Perhaps a shakeup will bring some new life into the show for me...
Of course, maybe I'm just crazy and there's in fact, nothing wrong with things as they are... who knows... I guess time will tell on that regard...