Definitely Brock and Cilan. Meeting between two oldest and most wise members Ash traveled with would make for fantastic interactions and i always wandered who is better cook between them.
Never mind scratch that, battle between those two would be much better.
I was also always interest in Misty meeting Paul. Dunno why but his arrogance and cold attitude would lead to interesting characterization and conflict from Misty side always having low brink of tolerance toward such behavior. It wouldn't be first time she tried to stand up to weak not letting that others underestimate her.
I will say i was curious to see how she would interact with Dawn too.
Max meeting Conway would have been interesting too. Both are bookworm type of characters showing to know lot about pokemon and strategy, having lot of things in common which could make for spicy dynamic.
Not really. Seeing a fishing lure isn't a big deal. Its not like Dawn (or even Ash or Brock) even mentioned Misty again the rest of the time Dawn was there.
Hell, the fishing lure itself never appeared again afterward, even though there were a few more fishing scenes in DP.
Should we than say same thing about May meeting Dawn?
Reason behind meeting was to get know Ash former traveling companion, to bring more continuity in DP story by letting know younger generations about Ash past and to possibly either advance Misty or Dawn story through that meeting.
Judging by all those flashbacks of Ash releasing Butterfree Pikachu refusing to evolve in Vermillion etc it surely wouldn't hurt to add extra reference to past.
Approach of "nothing needing to happen" only derives from point of story having more substance to it and it discourage positive discussion with return of previous companions only bringing extra benefits.
Main reason why so many people thought how Misty will meet Dawn is exactly because of that lure with Dawn eagerness to find more about her being annotated as some form of foreshadowing among people. Back than no one knew it would just stay on lure.