I'm a bit of an anti yoga nut Damo. I don't reckon they use anywhere near enough core and they stretch a whole bunch of things that aren't that useful to climbing and I would never recommend it as a climbing workout. Variations on planks are the way forward. And you use them heaps. they hold you solid in almost every position you in, any time you feel remotely barndoory, it's your core holding you on, when your feet are about to come off, it's your core holding them on. In fact, it's your core connecting you to your legs which you might have noticed are rather useful for pushing ... I really notice it's when my core has gone that I can't pull moves that were not a problem earlier in the day and I can't crank as far.
Some of the best climbers I know have never looked twice at a fingerboard. Many of the not so good climbers I know use them obsessively. They might have a place for the Adam's and Gareth's who were already onsighting 25 and trying to get better (and I am amazed that neither of them have injured themselves on their training regime) but most climbers are not Adam and Gareth. Most climbers climb 18 or less. Fingerboards are not what they need to get better. You can build sufficient finger strength just by climbing easily into the early 20s. What 22s do you need fingerboard training for?