The 3124's are great preamps, and I love working with them. I've done records with nothing but those, and they work great with pretty much everything. That being said, no, you absolute don't need any 3124's or any other high end gear to make a killer record. Anything that sounds clean enough and provides enough gain will get you there.
I might get a bit of hate for saying this, but in my opinion, you can get away with a lot more if you mostly work on modern metal than, say, acoustic music or retro rock. If you think about it, you usually have hugely saturated guitars, distorted bass, digital synths and drums that often have samples at least layered on there. As long as your preamps are clean and give you enough headroom, the little nuances from "coloured" units are much less apparent than with material where you're listening to a more natural, unaltered sources. Not saying you won't benefit from a good arsenal of API preamps when tracking a metalcore album, but you know, the benefits might not justify the cost.
