I believe that some dreams may be significant; they might be your subconscious working through an issue that you can't face or resolve in the awake state.
Then I've noticed too that many dreams are just your mind sifting through memories and events, sort of like defragmenting your hard drive. I have also noticed that when I do alot of an activity, that it tends to set a theme for my dreams. For example, when Nintendo first came out, and I started playing Super Mario Bros., I used to dream that I was the character punching blocks and stopming goombas. When I worked in a grocery store as a checker, I used to dream that I was cashiering--these dreams were dreadful, borderline nightmares as they never ended. I really hated that job, so maybe that was my way of trying to get myself to see that and get on with my life. I didn't though, I stuck with it for ten years.
If I whatch a movie that interests me, I can have dreams in that "format".
I think that in general, dreams are only meaningful if the individual can find meaning in them; that sounds like circular religious "crap reasoning", but it doesn't have to be. If someone flips you off in traffic, and you frankly don't care, then his gesture has no meaning to you.