North and the SEP have been discredited, but I disagree that this automatically makes reading the polemic superfluous. As I said in my initial post, the polemic isn't all about North and the SEP. Quite a bit of it addresses such things like the importance of the dialectic and Marxism's relationship to psychology, among other topics.
Also, while I agree that we can easily draw attention to North's anti-unionism, I think that's the easy way out. The SEP can't be reduced to North alone, nor do I think that North engaging in business is sufficient enough to discredit him. If I recall reading as such, Engels was a businessman as well for a time. The party's political line should be the main target here, in my opinion. North is only the tip of the iceberg. I urge you to read at least a little of what Steiner and Brenner have to say, if you have the time.