I half agree with this. I mean, if you're just giving a temp score, no further direction and telling the composer "off you go!" then yeah, I definitely agree with you. But if you take the time to say "hey, I like the rhythm of this piece" or "can you do an arrangement instruments like this piece," and that sort of thing, a temp score can reall help communication. Let's face it, music folks and film folks don't always speak the same language. There's a lot of cross communication learning that should be done on both sides!
I don't expect a director to say "hey can you do a modal shift on the viola line at measure 23" but that might be what they want. For them to say "hey, can you do something like this piece does at the 2 minute mark?" is an effective way to communicate. Gets everyone on the same page! So familiarizing yourself with different types of music, and as Gonzo says, experiment by just dropping different things in place, is definitely a good thing.
Of course, I've worked with Directors who have just said "that's wrong" until I came up with something that was barely distinguishable from the temp score, so you definitely don't want what you're hearing to be locked in to that. But directing the composer to get the emotions you want to convey correctly is a good thing, and at the end of the day you should end up with music that you are both happy with.
So, yeah, listen to music, try stuff out and don't let yourself get locked in to specific melodies. And treat your composer well