Favorite NT type: xNTP. Love ENTP's, but have to get away from all the energy after a while. Other INTP's and I have hilarious conversation, but I find them really lazy (and they probably find me the same way).
To simulatedworld, I really do think that it's possible that the INTP's you know are not representative of "us". That's not to say that I haven't had my share of problems when it comes to over-relying on Ti - because I have. I've read some of your posts in the past on this issue and you make some VERY good points - points that I've really considered for my own behavior.
What you don't seem to acknowledge, however, is that when your INTP friends make you laugh and throw out hypotheticals and you engage in back-and-forth banter with them (in other words, when they do the things that make you like them as friends), that is their version of Ne. At those moments, you are witnessing them use their secondary function that you say we never use and don't value. We do value it, we just aren't nearly as competent at it as you are. So, to you, our Ne seems inferior, under used, and maybe even weak. So, it's not that I don't value Ne or that I don't ever want to use it because I really do. It's just that my version of Ne is like a mini-me version of your Ne. We should always strive to develop it and become more competent at using it, but it's still our 2nd function compared to your primary.
On the flip side, there are ENTP's I know where I've definitely observed that their Ti is "weaker" (for lack of a better word) than mine. It's there - I can definitely see it (just like I'm sure you can see Ne in your INTP friends) - but, you ENTP's are not using it to the same level that we are. But, that's understandable, since it's only your 2nd function. I wouldn't expect you to exercise Ti like I do.