is it still beneficial if I do strength (weights) training only twice per week? (I run 4-5 times per week). I want to prevent injury in my legs (for running) and strengthen my upper body as I use it very little in running.
Definitely. Studies are showing that strength training enhances runner's performance. Twice a week should do it as long as you are doing full body routines. Work with free weights to get the biggest bang for your time. Remember that running doesn't stress the muscles the way a strength training routine will. Strength training usually prevents injury because you're not over-training your legs through running. The break and focus on tendons, joints, and muscles help develop you even more.
I like running, but it is stressful on the body. A couple of days of a solid weight routine will bring nice results.