Depends. I went from HD212's which were my headphones 4 years ago when I started to get into headphones. After some time I got the HD558's, and that was a good step up in quality of the sound, but I can't say I enjoyed listening to the music more. Critical listening obviously improved, but enjoyment? Nah I don't think so, and with some music the enjoyment went down. After that I had (and sold some of them) HD650's, K701's, Q701's, DT770's, DT880's, DT990's and T1's. I can't really say any of them gave me a "wow" moment or experience that I've always expected to get back when I decided I'll start investing into my headphone setup. To be perfectly honest, each of my journeys trough head-fi more often than not ended with disappointment and that horrible "wait, this is it?" feeling. Do I enjoy music more on T1's than on the HD212's? Nope. Do I appreciate and respect the sound quality more? Yes. Is it really worth it to me as just a listener and not a professional? Nope. And to be perfectly frank, I infinitely prefer my cheap dorm room speaker setup to my headphone rig. (speaker rig consists of a 15 year old Philips receiver that was cheap when new and a pair of Wharfedale Vardus 100 bookshelf speakers, some of the cheapest 6.5inchers you can get on the market, while the main headphone setup consists of Musical Fidelity M1DAC and M1HPAP + Beyerdynamic T1, costs 10 times more than the speaker setup). I simply think that the headphone rig can't even come close to my speaker rig in terms of emotion, involvement, naturalness, realism and the feeling of "being there". I can close my eyes with my speaker rig and feel the singer in the room with me. He has a body, he has presence, height and depth. I don't really get that with headphones. All of the stories and over-exaggerations of "soundstage" with headphones, even with HD800's or K1000's fall into water when you hear a properly set up stereo. And by properly set up I mean having speakers placed in such a way to form a triangle with your head. That is enough already to beat any headphone out there in terms of imaging. I'd argue my old 30 dollar Logitech PC speakers set up in such a way have better imaging and presence than my T1's, and I don't really care what anyone thinks about that.
So, is it worth it? I don't think so. Because, looking at myself right now, after going trough about 60 pairs of headphones in the last 3 years, I'm still not happy with my current rig, and every time I use it I still feel like something is missing. It's hard to explain to you since you haven't experienced it yourself yet, and you have that upgrade bug inside of you that keeps telling you that if you buy something more expensive it's going to be a lot better. It's not gonna happen. It's hard to accept that, and a lot of people will over-exaggerate things in order to make you think it does happen, or in order for them to justify their own spendings, but truth of the matter is, headphone hi-fi is VERY expensive, hugely expensive for what you get. Diminishing returns kick so hard in this business it can easily knock you off your feet if you're not careful.
So my advice to you is (which you will not follow since you have the need to satisfy your curiousity, and looking back at myself 3-4 years ago, I would do the same thing) keep the HD598's, get a cheap amp and DAC that doesn't cost more than the headphones themselves and enjoy the music. Invest into music, not gear. Don't let this hobby turn you into a hardwarephile, which most audiophiles are. Unless you have A LOT of money, so much that spending 500-600 dollars for headphones means nothing to you, go forth and upgrade, but in order to get any sort of jump in sound quality that will actually feel like you've moved a step up, you'll need to go for HD800's, and even then, it's going to be hit and miss depending on music.
EDIT: I know for a fact a lot of my friends from a local hi-fi club in my country have a similar oppinion. I know loads of people who went crazy with their HD800's + Lehmann BCL setups when HD800's came out, and all of them now agree that it was kinda pointless and if they could, they'd keep the money. The funny thing we were talking about just last week is how most of us are actually too lazy to get out the "good" headphones out of their boxes. And that is true in my case. A lot of times I just don't feel like it's worth getting up from my chair in order to open the T1 box, get the headphones out, unwind the cable and plug them into the amp....and then having to be ultra careful how I put the headphones on my head, how I put them on the table in order to not damage them, how I have to adjust them for 20 seconds because the sound out of them is super sensitive to placement over the ear, and then when I open my mouth or talk, the headphone moves and screws up the fit, so I have to usually keep my head movements nice and smooth in order to keep the headphones exactly on the spot where they have to be... and when I'm finished with listening, I have to roll up the cable again, make it fit inside the case, etc. It's too much fuss and frustration if you want to keep your headphones in good condition, especially if you have OCD and want to keep things perfect....whereas with cheap headphones, you just don't give a damn....you throw them around and don't care, you just focus on the sound. So most of the time I just keep my 25 dollar HD202's on my head and listen to music like that, it sure sounds good enough plugged into a 1700 dollar dac and amp combo lol.
you always try to hunt for something new, better, improved but in the end you end up still unsatisfied and wanting. I revisited some of my earlier purchases recently and was quite shocked of how good they were/are and thought,what on earth drove me to buy more gear?
