Value in the labor theory of value is taken in a generalized form, essentially an aggregate of all the differing labor times would be averaged into the value of something. The differences in the rate of labor can effect prices, but because of the market, all capitalists try to discipline and make more efficient their labor, so as not to be the loser in the market place. In another thread, an anon described the value as a "center of gravity" for prices, and I thought that was a really good metaphor. They all try and get that sweet spot of value.
As for art and books, socially necessary, and necessary for survival are different things, and if there is a demand for art and books, there's going to be a supply, but these aren't really things that are made by capital, but made by artisans, unless they are mass produced, in which case they follow the laws of commodities, where the value comes from how much labor is needed to make enough of them to meet the demand. I would imagine they'd fill a role like the luxuries in V.P.P.
All societies that have a division of labor must make a surplus of things, since all things are not accounted for by yourself. I don't know how the USSR used this surplus though, sorry.
There is a good YouTube series, called The Law of Value. It is, I think, pretty good at explaining things like this.