Is heavy vinyl worth it?

Heavy vinyl usually accumulates much more statics than regular. In case with 150g you can get away without VTA adjustments while 180...200g will likely need it.

I set my TT up using heavy/thick LP stock and add a second "slim" wool felt mat when playing thinner LP's.

I do not hear much of a difference between thick VS thin LP's as long as both are flat and in good condition. My TT is located outside the listening room, I use a non-clamping LP weight and I do not listen @ high volume levels (which may have something to do with this).

The only big step "up" for me (amongst recordings that are decent to start with) are the 45 RPM versions.

Complicated. The old problems were crappy vinyl, thin pressings and uncontrolled cooling or curing. The new problem is, can a re-issue be done to at least approximate the old stock (or even do much better, like fixing the wrong speed). I have late 70s early 80s that are so thin the sound bleeds from the other side. No wonder the CD people found ready targets. Most new is on 180-200, which can affect your tip attitude and sound less then it is. You may need to lift your arm a tad to lock back in. Course that is a problem for your regular LPs. My last comment is that it is the maker more than the thickness.

Yes.

The special pressing with heavy vinyl are better for us. Matering from Dcc (vinyl) and others is even more important. But your mileage may vary. :)

Al

IMO, the weight of the vinyl isn't much of a determining factor, and the extra-heavy audiophile pressings may be better because of their vinyl stock quality, and the mastering and pressing care that's taken, but the actual thickness of the record doesn't have much to do with it. I feel the extra weight is mostly a marketing tool, and can interfere with effective clamping, not to mention the inconvenience of readjusting VTA should you feel the need. Standard weight is fine by me.