Sequels are useful for a novice player because they can really give your games a boost. This can make a huge difference in your review scores. However, for the strategy applied in the game, they are unnecessary and can even be a detriment by improving the quality of your game too drastically and too quickly for you to continue your consistent improvement without another sequel.
If you do choose to make a sequel (particularly very late in the game when your staff can't improve themselves much), remember that sequels should be released at least 40 weeks after the release of the original and should always use a newer engine than the original. Failure to do so will result in a penalty.
