I think it's important to be a bit of both. I know a lot of people that follow mainstream fashion simply because it's "fashionable" and not because they actually like to wear the stuff. Personally, I'd hate to wear something I'm not comfortable in, or don't like the look of.
Coming back to the question, what I mean by "trend setter" is, do you like to be original, or do you just wear what's "in"? Personally, I'm on the fence on this one 'cos at my age, it's more about what's comfortable rather than if it's fashionable. Also, I think you start preferring accessories over clothing when you get into your 30's/40's, well I do anyway, I can't speak for others.
It was my daughter that actually prompted me to ask this question. She just went 13 the other week, if you've got kids you'll know what they're like at that age, getting into the whole makeup malarchy, oh dad I wanna go shopping here, there and everywhere, dad please buy me these shoes, all the girls at school wear them. And, I thought really? Why would you want to wear something that loads of other people wear? Does it not just become boring?
To conclude, I think it's very important to think for yourself when it comes to fashion 'cos I think what you wear does reflect your personality. What does everyone else think?