I'm by no means at the audiophile level as most of the posters here, but my current setup is a pa2v2 with DT770/80, so I feel I'm somewhat qualified to answer here. I bought the phones new on ebay from guitarinsider ($200) and I feel that they are worth every penny. Again, here, its all dependent on what you use them for.
In terms of your mp3 bitrates, you will be surprised at what a good set of cans reveals. You will definitely notice a difference between your 128/196 kbps mp3s and 320 kbps, provided your source is decent (and it sounds like you are getting a decent sound card, so it should be). I wouldn't go so far to say that these mp3s will be BAD by any means, but the cans will bring out flaws in the music that you may have not noticed before, especially on speakers. I know a lot of my old, pre head-fi.com mp3s are of a low quality, and I went back and re-reripped them in 320kbps. Even this isn't the BEST solution, but it sounds fine with these cans.
I think that your music tastes will probably work well with these phones, at least if you prefer heavy bass. The PA2V2 will even intensify this bass, so if you want to tame the bass on these you might even want to look into a different amp, although for the price, the PA2V2 cannot be beat. If you want to tame the bass and highs, you could consider having them recabled at headphile, but recable +woody can easily run you $250 there.
I love these phones, but I understand that they aren't for everyone, or for every type of music. If you like a lot of classical, I'd say look elsewhere. But if you want a closed phone that can handle gaming, with or without an amp, and love bass, these are probably the phones for you.
