Are these parallels thirds/sixths legal?

Generally that seems rather accurate, but just two comments:

- Parallel fourths are entirely different form parallel fifths. Fifths melt together a lot better than fourths, which is why traditionally the fifths is considered a perfect consonance, but the fourth a dissonance. So there's no problem of "vanishing counterpoint" when you have parallel fourths. They are only "not ok" in classical counterpoint because they are unresolved dissonances.

- I'd be extremely careful with saying that a particular technique is "not musically interesting". Parallel fifths can be problematic for contrapunctual hearing depending on the nature of the counterpoint, but there certainly is musical interest outside of counterpoint. Sound and timbre, for instance. And exactly for these aspects, intervals that "melt together" are extremely important. In music that focuses mainly on colour instead of contrapunctual lines "parallel fifths" have an entirely different meaning.

You might correctly point out that in such cases, where it's not truly contrapunctual it would be wrong to talk about "parallel fifths" in the first place. But it's not always strictly the one or the other. There is quite some music that fluctuates between "sound colour" and counterpoint, which can be an extremely interesting combination, if used well.

And to get back to the point of this thread, yes, parallel fifths and octaves are a different problematic than parallel thirds and sixths, but the fact that parallel thirds were always "allowed" -doesn't- mean they're "appropriate" for every style. They may not "kill" counterpoint, but they can severly limit it. They are not something that you would commonly find for extended periods in very dense, very contrapunctual music, as they too give the impression that two voices are "bound" to each other, where classically counterpoint seeks to display the seeming independance of voices. ("Seeming" because they are of course usually still connected in rather strict systems, harmonically or otherwise.)

So in summary, I think it's problematic when you focus too much on certain musical rules, like "You should always do A and you should never do B". Those rules may have good reasons and it's good to know them, but in reality it's often much more ambiguous. But as I said, I don't think it's any problem in this piece here.

Sorry for this kind of frivolous response, but this MIDI reminded me a WHOLE lot of the song "Less Talk More Rokk." Search for it on seeqpod.com and listen to it if you haven't heard it, and you'll know what I'm talking about

Yes - I do see what you mean!