Mike Beggs:
"Isn't the essence-phenomena divide a little undialectical?"
I don't think so. All of these philosophical categories tend to harden up into formal distinctions if you don't keep in mind that they are only moments in the flux, of course, so I would not say 'divide'. Still, without manifestation, there would be no possibility of movement. And, as Marx says, if essence and appearance coincided, all science would be superfluous.
Mike:
"I think if value exists it's immanent in prices, wages and profits, not 'more real' than them."
I can go with 'immanent', and I would not say that value is more real than every single instance of price in aggregate, but it is more real than each single instance of price, since each instance of price is subject to accidental and conjunctural factors - the recent rise and crash in banking credit being an example.
'But in a lot of ways the Vol. 1 conception of value at least is not real, but is an epistemological device, an abstraction.'
It seems like a lot of time to spend on something that is not real. The way I see it, the value, i.e. the labour content, is the more real thing than the price that the good happens to find on one particular day. (Of course, we might discover that our painstakingly hand-loomed cloth is just junk, but that is why Marx differentiates 'socially necessary' labour from labour as such.)
On my reading, 'epistemological device' is not right. Abstraction, I could go with, but on the basis that this is a real abstraction (see Ilyenkov), meaning that the intellectual abstraction works because it mirrors, or reproduces in thought, an abstraction that takes place in society. So, for example, Marx says that the category 'labour' is acceptable in theory, because it mirrors an actual abstraction, the one that takes place on the labour market, that reduces all those different activities to the one undifferentiated mass of labour.
'Value' after all, is not something that Marx thought up. It is not as though it was something that he could have named arbitrarily, calling it Kryptonite, or 'factor X', for example. Everyone knows that there is real value behind the accidental price that the market sets - which is why you always get a few estimates, or make some price comparisons, before you buy or sell.