I think this may all depend on exactly what YOU want. When it comes to composing for media, you kind of have to be versatile. But the most important thing, you should LOVE doing what you are doing. It should never feel forced. I experienced this a couple of months ago. I was contacted by someone who wanted me to write reggae music for a singer of his.

Now, I absolutely LOVE reggae. But... I love traditional reggae. And traditional reggae wasn't what this guy was looking for. He wanted more of the mainstream reggae that I am not too fond of (plus his singer used a lot of electronic sonorities that I highly disagree with, like autotune, plus I wasn't impressed at all by his lyrical ability).

Needless to say, I didn't work with them, and the reason I didn't was because the more I wrote, the more I started to despise what I was doing. If instrumental rock is what feels right to you, do that! There are going to be projects out there that are going to need it. Heck, I had a project where I was doing a instrumental old school, westernish rock soundtrack (of course it fell flat on its face), but had it pulled through, it would have been a pretty sick game. But, more importantly, if you do what you love, and do it well, people will come to you wanting music, be it playing at venues or writing for a game.

Oh, by the way, I'm really digging the heavy stuff man. One dream I've always wanted to make a reality was performing in a metal band. Something like Gojira! (I think I'd be a pretty good rhythm guitarist, but I'm not really good at lead)
I hope you start another one! You guys had potential.