It's going to sound strange but running slower will make you faster!
On your longer runs try listening to your breathing - it should be calm enough to be able to chat without pausing for breath.
Running slow enough to keep your breathing relaxed will encorage adaptation that builds aerobic endurance which is the key part of running long races like half and full marathons.
That's excellent news :D I usually run with a buddy, and we chat the whole way, without breathing mid-sentence. I guess I'll just keep it up. What's your take on interval training?
Useful - if anything just to give your body and mind something different to work on.
It's less important than low effort runs or pace practice and carries more injury risk (make sure you warm up properly) but it can help build strength and work on your running form.
I usually ask my runners to do an effort or hill session once a week.