I've got the crossfire, had it for just under a year, use it commute every day, very very pleased with it. The Vulcan was not out when I bought the crossfire, now having ridden a colleague's, and enjoying, I'd be now facing the same dilemma as you are. If you are ever likely to want to go off road, then the crossfire-e will handle paths and light trails, the vulcan is of course gonna be much better on the rough stuff. There's a YouTube video which you have probably seen on a guy throwing around the vulcan, getting air on jumps etc, very impressive. I'd go and test ride both, if you are happy with the vulcan on the road, then maybe that's the better choice. As you say, you can throw on some road ish tyres. Just make sure you are comfortable on either... Normally you'd go for a smaller frame with a mtb, than a commuter/road, I've got the largest crossfire (21in) but would go for the largest vulcan, 22in one, as the one I Rode was the 20in one, and felt a tad small on the road, but ideal off road. Good luck
ps. If I could smuggle a vulcan into the garage without her indoors noticing I'd get one to go with the crossfire-e lol