The period at the end of the last sentence of the last docuмent.

I don't think any doctrine was well-developed at the Vatican II pseudo-council.

Much has been discussed about the Modernism of Vatican II, but what's are Vatican II's best doctrinal developments?

That's like asking which animal's shat smells the best! 

For those Traditional Catholics, however, who believe that infidels can be saved ... well, Vatican II does an admirable job of laying out the ecclesiology behind such positions; these Trad Catholics should consider the V2 "subsistence" ecclesiology to be both brilliant and sublime.

That means the Novus Ordo, SSPX, and all of the major sede groups for they all agree that Pagans, Jєωs, Mohamedans, Hindus, Buddhists...…. can be saved by their belief in a God that rewards. The individual priests might not all believe it, but it is taught to them as "dogma" in their seminaries, and if they question it, they get the boot.

As an aside, I haven't read a lot of it.

But you can tell just by the implementation of it that something was off. If they meant something theologically sound, it was overshadowed by the aftermath — 50 years of crumbling parishes, sinking vocations, and bad, neo-Marxist theology.

I have read most, maybe all, of the docuмents.  It is a characteristic of pretty much all of them that they contain enough ambiguity to be easily interpreted in a heterodox way.  This is what made it possible for the implementation to be so horrible.  It is not really possible to talk about its "best doctrinal developments".  About the best that can be said that it is capable of being understood in an orthodox way by those who have the will to do so.  And even that is debatable.  

As if this weren't bad enough, this sort of ambiguity continues throughout the subsequent Church docuмents, making it possible for Catholics to hold any number of heretical positions while claiming they have the approval of the Church. 

I can't believe that a Traditional Catholic asked this question.

Tradition stopped in circa 1960?

For example, it did mention Mary more than any other council and said Gregorian chant should be given pride of place in the liturgy.
Was Bp. Fellay wrong in saying that 95% of the council is Catholic/orthodox?

Gregorian chant is an excellent example of the problem.  Look at Sacrosanctum Concilium 116:

The Church acknowledges Gregorian chant as specially suited to the Roman liturgy: therefore, other things being equal, it should be given pride of place in liturgical services.

But other kinds of sacred music, especially polyphony, are by no means excluded from liturgical celebrations, so long as they accord with the spirit of the liturgical action, as laid down in Art. 30.

The first half sounds great (although even it is weakened by the phrase "other things being equal").  But then the second half undermines it to a point that people can do the opposite.  We are left with the vague expression "accord with the spirit of the liturgical action".  In effect, the endorsement of Gregorian chant is permission to do just about anything.