I would be more worried about the drive than the game DVD. You should probably take it out when not in use.
If you are often using the disc because you play the game a lot, you can try doing this instead... Make a disk image of the DVD using Disk Utility. When you play the game, mount the disk image, instead of inserting the DVD. Because it's a disk image, there is no wear and tear on any physical disk or drive by leaving it mounted all the time.
Some games will look for the physical disc so this will not work, but it works for a lot of the games I play. It may also be a problem if you are low on disk space.