Thinkers are no more concerned with ideas than Feelers are. Intuitives are more concerned with ideas I would think, though they are no less concerned with feelings or experiences. Maybe introverts are too, I'm not sure.
You are right, and my comment applies more to NT vs NF, though a parallel comment might be made about ST vs SF. See below for more on the distinction.
Self-centred... selfish... ego-centric... whatever, Thinkers are less likely to help others or compromise their own position for another. This is going to lessen the quality of your relationships. This lack of interest in others is essentially the defining feature of a Thinker.
No, it isn't. The defining criterion is objective vs. subjective judgment. A feeler can be very self-centered, refusing to compromise his/her own subjective values in favor of another person. A thinker, on the other hand, can see the logic in someone else's position or realize that it really does make more sense for him/her to do something that helps another. Self-centeredness is separate from T/F, except that how and when it manifests will be different for each case.
To get back to NT vs NF, this distinction applies to the shared ideas. When I share with NFs, their ideas are filled with values and emotional considerations. NT ideas are filled with logical connections, cause/effect, and more objective considerations. I think of the second as "ideas" and the first as "feeling", partly because that's how some of my NF friends describe our interactions, but "idea" could include all of it, with the distinctions mentioned.
An example:
An ESFJ values good relationships and wants people to like her. When she interacts with others, she essentially "tells them what they want to hear" so they will see her in a positive light. She compliments them, even if it isn't sincere. She makes promises, but later does not keep them if it is inconvenient, always having a "good excuse", of course, even if it isn't true.
An ISTJ is quiet, not too sociable, and occasionally just blurts out "the wrong thing" because it is true. He recognizes all this and has learned to hold his tongue at times. He always considers how his actions will impact others (cause/effect analysis). When he makes a promise, he has thought it through enough to know he can keep it, and he does.
Which of these will have "better quality" relationships?
(BTW, these are real people I have known.)