A few years ago when I was serving as a Resource Minister in our Region I was asked to fill the pulpit in one of my churches for a couple of weeks. I used to joke that I really only needed five sermons as a Resource Minister since I was usually in a different church every week. Since I would be in a different place the people there would not have heard the sermon I did the previous week in a different church.
On the second Sunday I was scheduled to preach in that church I decided to preach one of my favorite sermons even though I had preached it in that church seven years earlier. Few people remember a sermon more than a few weeks at the most so I wasn't worried. After the second service in that church a teen came up and asked, "Didn't you preach that message here before?" Busted! All I could do was smile and admit that I had.
There's nothing wrong with preaching a sermon over again in the same church. After all, the church sings the same hymns and songs over again. If a sermon is worth preaching once it's probably worth preaching again. Sometimes.
When I began my current ministry as the Transitional Pastor in a church I was convinced that sermon preparation would be the least of my concerns. After all, I had been a pastor for twenty years and had a file drawer full of sermons I had preached in my previous church. However, as I've gone through them I've discovered some problems with most of those sermons.
One, many of them are outdated with illustrations that have no relevance to our culture today. Two, most of them no longer reflect my preaching style today. Three, the majority of them lack the scholarship I now want in my messages. Fourth, few of them are pertinent to the church I'm currently serving. They were addressed to another church for another time. Almost none of them are suitable to preach in my current church.
Occasionally, I'm able to use one for inspiration and can sometimes use bits and pieces from it as I prepare a new sermon on the same topic. That's what I would suggest you do with your old sermons. A sermon that is not culturally relevant is of little value and will lack the impact on the congregation that you want.
There's nothing wrong with preaching a sermon over, but before you do check it over and make sure it will still communicate the message you want today's audience to hear.