I think NT's are classy and eloquent when they concern themselves with (and make a priority of) things like harmony and being a team-player. When we get all wrapped up in "being right" and always coming back over the top of someone (which we are very prone to do without even realizing we are doing it), it is in those times that we are moving away from class and eloquence.
We have good solutions to problems. We think things out very well. We can be very good at whatever we set out to do. That's all fine, but I think it's when we humble ourselves and "include others" (this is very broad) that we then have class. Start a business that you're passionate about - not just for your own pathetic gain that you can't even take with you when you leave this place, but start it for the employees that you will treat right and pay well. Start it for the customers who will love your product and your service, who will see you as an organization who does things the right way.
Another example in my personal life (and perhaps it's common with INTP's) is let's say a friend is throwing a birthday party and wants me to come. I really don't want to go because there will be lots of people and interaction and it all just seems like a big headache to me. But, I've learned that situations like this aren't about "me" and my being inconvenienced. They are about a friend who genuinely wants me to be at his/her birthday party. Me being there is important to them. I don't always make it to these events, but I've begun to see the importance of stepping out of my own head and being giving of myself and my time.
In short, I think we move closer to class and eloquence in moments where we lose our own selfish ambitions and "what's in it for me attitude". When we give of our time and give of ourselves (while still using our strengths and being true to who we are), that's classy.