Hi Littlest Goat,
I too make most of my cheeses from raw goat milk, and have noticed the same variation you talk about. It was driving me crazy - I would make two batches by the exact same method and one would be a perfect chevre & the other would be a dry crumbly mess. Then I started reading this forum a bit and realised that the variation is more likely due to the milk itself, than to any minor differences in method. When using raw milk, it contains a bunch of naturally-occurring cultures which can affect the result if they are not killed off by heating/pasteurising. But even if there IS a heating step, they can still affect the end result because they have changed the pH of your milk - i.e. the milk has started the process of going sour. This is all just a long-winded way of saying that I think older milk can create drier curds, which will not hold together as nicely. This is just a theory though - there may be some other explanation that I haven't thought of. As I have pretty limited milk supply, I tend to just adjust my cheese type to match the milk's properties - so if it's making fat rubbery curds, I'll make mozzarella or paneer, if it's making fine soft curds, I make chevre or feta.
Another tip for using goat's milk is that it can be harder to get nice big curds, than with cow's milk. Sometimes you will need to add quite a lot of vinegar to get decent curd formation, which will make the cheese taste overly-sour if not rinsed. Adding calcium chloride is supposed to help with this - I have never used it (just got my first bottle in the mail today!), but I've also heard that just adding plain salt can help the curds to form too, in cheeses where this is appropriate. I'm not sure if this is backed up by anything, but the reasoning (i.e. that dissolving more stuff in the whey will help to "force" the curds to drop out of solution) sounded plausible. And I salt most of my cheese anyway, so I figured it couldn't hurt.