to work on one area of training per day or could you actually mix a little of everything on every ride?

I find it very difficult to accomplish working on a certain training item per ride. Hill repeats are easy, I can do 10 of them before boredom or fatigue sets in. What I am most interested in bettering in my cycling is my speed/strength/endurance in climbing. Are hill repeats a required 'to do' item on your weekly training list to build or maintain form? I am really just starting to get interested in other areas of cycling, like targeted training for bettering specific areas. I've been cycling since Sept 15 and have 2500+ miles so far with lots of different riding. But according to everything I have seen, climbing is my worst area, funny though is that it's my favorite because it is so challenging. I change up my repeats each time between cadence, gear, standing and seated. Sadly I have not done them in a couple of weeks... but am tomorrow morning.