No real inspiration exactly, it was mostly me being handed a 7, and liking it. A lot. And I play primarily in a weird tuning that's really complimented by the extra string, so that just added more want for one.
Good ol' Korn. The first song I heard by them was Good God off of Life Is Peachy and the lows just sounded so brutal in that song. At the time I had a shitty Harmony 6 string from a JCPenny catalog lol....so bad. But the summer of 1998 I saved up and bought an Ibanzed RG7420. That guitar was the shit and I promptly learned the first 3 Korn albums...well what I could play without the effects at least.
After Korn it was old school Chimaira and the Pass Out Of Existance album around 2002. That's when I got into syncopation and playing chuggy like that. Then not shortly after I heard Future Breed Machine by Meshuggah for the first time and had absolutley no idea what the hell they we're doing with timing and what not and it was around that time that Nothing came out and the 8 string thing blew my effing mind. I still don't really dig playing an 8 too much, but I remember hearing that low string on Stengah for the first time and it melted my face off.
I was always into 7 stringers like Broderick/Loomis and I loved Trivium's Shogun but the guy that really pushed me over the edge into wanting one for definite was Andy James, the man's a monster player and manages to sound musical all at once, huge influence on me.
100% reason i bought a 7 was to play dream theater tunes. My friend and i decided that it was imperative for me to get a 7 and him to get a 5 string bass. I might also mention we havent actually covered any 7 string DT songs ever lol. I wanted to play panic attack but everyone said it was too hard so i was like "okay whatever".