My boyfriend and I exchange "I Love You" a few times each day. I don't think a phrase like that loses it's meaning. When I say it, it's because I truly love my boyfriend. When he says it, I feel like he truly loves me. I used to think that we said it too much, but if I didn't say it, my heart would explode from all the pressure of holding all that love in.
Some phrases are over-used for the sake of starting conversation, and those might lose their meaning.