I've not had practical experience of this myself but from my RF days there are two things I can tell you. First is that adding a higher gain antenna should give you a better signal and hence (all things being equal) range. But that higher gain isn't free - antennas that have a higher gain than a basic model achieve that increase by concentrating or directing the energy in some directions at the expense of others. For example, few people find the energy that goes straight up into outer space to be useful, so a higher gain antenna might reduce that and redirect it horizontally, giving a 3D radiation pattern shaped more like a donut than a hemisphere. Antenna manufactuers will usually have diagrams that indicate how the energy is radiated and so what you need to do is consider this in the light of your installation to see if it might cause you any dead spots etc. Its unlikely, but I thought I'd mention it.
