I actually insisted with the guys from our site that we start to capture more video interviews. I think it's part of establishing our brand. We do need better equipment though, and next time, I won't wear a freaking polo shirt to interview a metal legend like I did with Blaze!!!
I just upgraded from a headset mic to a Blue Yeti USB one, it's extremely popular choice for streamers. It just works well, plug n play and not too expensive. Basically it's one of the best mics before you get into serious equipment. (this is not to be negative to you, just thinking if you want to upgrade equipment and since you do interviews, the mic might be the most important piece to upgrade first). I don't think your video quality is bad, but audio drives the video as my high school TV production teacher used to say.
And of course outfit is important but honestly, I don't personally see an issue wearing a polo shirt. I've gotten a lot of flack at metal shows for dressing more business casual (since I was coming from work) so I get why you might want to look more "metal" but IMO, I really don't get the whole fashion thing. As long as you don't look like a slob (which you don't).
Either way, I love seeing how you progress with the interviews. You've been getting bigger and bigger names, so it only makes sense for you to want to start upgrading the hardware for better quality.