It's better than zero that's for sure. In my years of training I have found that one a week isn't enough to have noticeable gains unless you focus on one specific body part. Since you are already running and climbing perhaps you could focus on chest on that one day. This would likely produce good results since both of your other main fitness activities are primarily leg and arm exercises. I think climbing seriously engages the back and shoulders as well but not so much chest.

It's just an idea.