The Prime Directive was a Vulcan thing originally.
My first reaction is to be dismissive of this (if not to dismiss) because it's ENT. But even in TOS it was a very Roddenberrian notion. That humans had learned (apparently to their cost) the consequences of trying to "fix" things. OTOH, in TOS the Prime Directive was not nearly so draconian as it would become in TNG. Friday's Child comes to mind.
I just realized that I have another nail in the coffin of the TNG Prime Directive: We have seen peaceful, happy peoples who's very existence must be left to doubt because of the "wisdom" of the Prime Directive.
But the Vulcans came across Earth in the mid 21st century, a planet that within the last decade or so had attempted to annihilate itself through war and violence on a truly global scale. But ONE GUY had figured out faster than light travel.
Hey, T'bam, Let's talk to THOSE people. They seem advanced.
Pre-ENT I prefer the notion that the Vulcans were there in an STL ship and they made contact because the monkeys had something that they didn't. Or go with the various histories pre-First Contact. But that ship has well sailed.
No, I don't believe Vulcan had Starfleet facilities. Being the TOS exclusionist that I am, there had to have been a reason that the Vulcan ambassador and his wife had to be ferried from Vulcan to Babel. Also notable is the Vulcan Amassador's distaste for Starfleet. This isn't a private citizen this is a representative of the Vulcan government. (And yet he feels that Coridan needs the protection that the Federation would afford by being a member. Very logical, Mr. Ambassador.) In TOS the Federation was very loose knit. VERY.
Are there any real world organizations where a member state has an "ambassador" to itself? I guess the UN (or NATO) analogy is more apt than the USA or USSR or Great Britain. Only with a para military / exploratory force. On the other hand we are discussing member "states" with literally planetary populations who are at best days travel from each other. (Please sit down, Mr. Abrams.)
I was going to say TNG made the Federation more cohesive, but even The Voyage Home gave us a President.
(Star Trek is weird.)