Well, I agree with you that they're both worth hearing in as many takes as possible, and if I had the money I'd probably snatch up all the recordings available too.
But comparing the two volumes to two "halves" of the Goldbergs is completely wrong.
For one thing, we don't even know if volume no. 2 is in fact volume no. 2 - AFAIK the title page
of the manuscript was never discovered, and we just have to assume that the title
would have been WTC simply because the structure is the same. And we're probably right. But we can't be
sure.
Another thing is that the two volumes were composed more than 20 years apart, and vol. 2 is written by a much older composer who is, in a way, summing up his (musical) life. So this is, in many respects, a more mature work (I'm not saying "better"!).
Also, the first volume was prefaced by a note stating an educational purpose of the cycle, while there was probably no such note in the second volume - perhaps Bach wrote this one with a purely musical goal in mind?
And last of all: these are two cycles. They were prepared by Bach as cycles, ie. each volume is meant as a separate, complete entity, so there's absolutely nothing artificial in treating them apart.
I find vol. 2 more appealing because for me it is much more poetic and "subjective" in comparison to the technical "coolness" of some of the pieces in the first volume. Needless to say, I love both of them, as I love and cherish everything Bach had ever written (at least everything that I've heard

).
Cheers,
Maciek