Is extremely accurate "VTA" adjustment necessary?

Certainly, 180 and 200 gram records are unusually thick, but there are not great differences among other records. Finding the right vta thus is not entirely dependent on which record you are playing. Some time ago when I had a Wheaton arm with calibrated settings, I went to the trouble of assessing about 50 LPs. Most had the same setting or very close to the same setting.

so much for having the last word on this subject.
I did not say perfect vta was theoretcical.
I said those who claimed they could find it easily and repeatedly by ear were highly suspect. A claim that offended many.
There is a perfect vta and that can be and has been proven mathematically.
I have yet to hear anything "snap into focus". Improvements were significant enoguh to justify the effort, however.
You are dealing with a very tiny stylus riding in a very narrow grove. I contend that the stylus is affected by movements so small most human eyes and fingers are incapable of making them. diamond cutters and jewleres exempt. Both diamond cutters and jewelers use very acuurate tools and magnifying devices as aids.
I read a lot of stero magazines in my day. I threw most of them away. My recollection of the first vta article was science based and not golden ear based. I beleive it was in the late seventys. Like most tweaks I was a skeptic. It was only 'till I got a system capable of resolving the difference did I beleive. Maybe (dougdeacon) you and others had already discovered it.
My comment about "worshipping at the alter of vta" was tongue and cheek. Come on, reread some of the descriptions in this thread about the benefits of correct vta. Don't you think they exagerate just a little.
If you really want gorgeuos sound get some triodes and electrostaics with a Koetsu rosewood signature.(okay!okay! adjust the koetsu for proper vta. by ear if you like)

LOL: "(okay!okay! adjust the koetsu for proper vta. by ear if you like)"

Thank you for the humor, Gregadd!
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As a point of interest given this extended discussion, 6moons.com just published a review of the Walker Proscenium turntable and an interview with Lloyd Walker. One of Lloyd's comments was about his design conclusions on adjustable VTA during play:

Lloyd Walker: One thing we discovered right away is that adjustable VTA during play is probably one of the worst things you could ever put on a tone arm.

Reviewer: Why? I loved it on the Graham arm and it spoiled me. The ability to adjust VTA while playing is certainly convenient.

Walker: Well if you notice, when you adjust some arms while they're playing and you run the adjustment up and down from top to bottom over the whole range, you'll notice some differences but it's not huge. You change the butt of the VTA on our table 1/1000th of an inch and you can hear it plain as day. It's enormous but every time you set the VTA, it's locked in place. The arm cannot flex or move. To adjust an arm during play, something has to be left loose so the arm itself is wobbly. When you're talking about trying to read information in a groove that operates down into the micron size, iron-clad stability is critical. If you leave an arm loose enough for VTA adjustment during play, it will flex and you will lose dynamics, information etc. You just give up too much music for a few minutes of convenience.

Reviewer: But other arms which have adjustable VTA during play have tight locking mechanisms.

Walker: Doesn't matter. When you lock it back down, it's gonna move because that lock's going to torque it to one side and that's not only going to slightly change the VTA but it'll shift the azimuth as well since the whole assembly is flexing to one side.

http://www.6moons.com/audioreviews/walker4/sota_5.html
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I totally agree with Lloyd on this point.

However, it could be argued that the problems Lloyd has pointed out might be minimal with certain tonearm systems, and the trade-off may be considered by the user to be a worthwhile trade of convenience in VTA tuning vs absolute stability and geometry.

In an absolute sense, Lloyd is correct on this issue, as I think would be expected of the producer of a turntable at the quality level of the Walker.