One of the most frustrating things about the modern Church is our incredible ability to dismiss certain scriptures because they came from the Old Testament. Although it is true that we are no longer under the law, as Christ fulfilled it, it is absolutely false that this therefore makes all the Old Testament somehow irrelevant.
A good way to think of it is this: History happened. You simply cannot change the past, and a significant portion of the Old Testament is just a recording of past events. This includes prophesies of Christ Himself, which is what Christ, of course, fulfilled. In other words, saying the Old Testament is somehow irrelevant, and discouraging its use, is actually as foolish as claiming you can change the past.
It would also erase a good portion of the New Testament, given how often it quotes from the Old. If you take away the Old Testament, the New Testament has no ground to stand on. Therefore, yes, it is entirely appropriate to revere, study, and cite the Old Testament.