You have clearly been on typec enough to know a thing or two so I'm not going to go into the fundamentals I'm just going to assume you know. I will only say that I know more than one INFJ/INTJ couple, fairly common when you factor in them being two of the three least common types. By contrast I don't know a single Ne/Ne couple and it would honestly disturb me, other Ne doms feel like family to me.
I've heard a lot of INFJs say "gross", "that's nasty" or "that's like incest" when talking about Ni/Ni pairings. To partly use something Synarch once said I/I couples have WAY TOO much self and E/E couples don't have enough.
I think you should get two magnets to illustrate this example, try putting the two -/- together and see how that works, now give the +/+ a try and you'll understand why you see two Is together but never two Es, because with the Es it's very clear there's an issue where as with the two Is they feel safe in a lazy sort of way. Now try the -/+ and you will better understand something that was very clear to Jung.
As for the introverting/extroverting where it relates to a Ne dom. People WHY ARE YOU NOT GETTING THIS! The four most introverted of all the MBTI types are:
ENTP
INFP
INTJ
INTP
Notice, you as an INFJ with a secondary Fe function don't make that list. Most introverted would be a Ti/Ne (that's makes perfect sense followed by a Ni/Te, Fi/Ne and coming in as the most introverted of all the extroverts...Ne/Ti.
I'm saying this because I keep hearing the same thing over and over again about ENTPs and it makes me question if the people saying it actually know one or if they just met one that was extroverting.
Picture the ENTP like the turbo charged introvert, it's there when we need it but sometimes you seriously need to talk me into using it.
Hell, Sunday I went out with my INFJ friend at a club and he was hanging in there, I had to walk out just to get away from people cause I couldn't deal with them anymore.