New doors can be a good way to improve the security of a property. However, are they really needed? This depends on a lot of factors. There may be other ways in which you can make your property more secure, without having to replace the doors completely.
First, look at the doors and see what condition they are in. If you are beginning to notice gaps and the doors are looking a little old, now might be the time to invest in some new doors. The doors will not be as strong as they need to be, and will be a hindrance to security. Their age will also show, making your property an easy target for burglars.
If the doors to your property are moderately damaged, it may be possible to repair them. If they are not damaged, you can install new locks (British Standard is advisable) or safety bars and latches. Talk to a locksmith about how best to go about this.