For the record, I'm running the Audio Unit version in Logic. I couldn't say about the merits of VST2 vs VST3.
On paper, there are a lot of things that I like about ST3 over ST2. As Bit said, the upgrade seemed like a no-brainer. But I remember that the fun began from the moment I started installing it and importing legacy instruments. In fact, I remember exactly how that night of late September 2014 was also wasted.
Fortunately, I have a sampler that covers most of my bread and butter needs and then some. But there are things like the Miroslav library which I would like to use. However, some of those patches don't seem to sound quite the way they did in their own shell or in ST2.
In fact, most of the libraries/instruments I would have a use for are part of those legacy add-ons, though I have also found more than adequate "native" alternatives for things such as SampleTron. I don't care much for "general MIDI" type of instruments, I don't need another mediocre honky tonk piano patch or average guiro sample.
Part of my frustration with 3rd party comes form the fact that we now need to install two times as much software as we want to use to accommodate every manufacturer's own mean of authorization. Waves have theirs, Cakewalk have theirs, FXPansion now have theirs (as I learned a few weeks ago when I decided to re-install BFD), etc.
Ultimately, I just don't like to be forced into installing and/or updating software. When I upgraded the studio computer, I decided to treat it like a hardware recorder and to keep it as clean as possible. I decided not to install a lot of the plug-ins I owned and to only install the essential.
In spite of that, I end up with a computer that's cluttered with a lot of software that's only there to allow me to run software which I paid for.
And yet, there are things I can't yet imagine myself w/o - I'm really liking Rapture Pro these days.