Great question and thank you for opening up the debate! You'll get a lot of good answers here. I read some of them, but not all so sorry if others have already answered your question but here are my two bits...
1. Is it worth paying for 24 bit audio files with 48khz or higher, as opposed to CD quality tracks with 16 bit at 44khz?
A) In my humble opinion, yes, but barely. Let me explain. I haven't done any single or double blind tests of music files when I'm not in my listen/reading chair with my good dac, amp, and headphones. But I don't think I would notice any difference between Redbook CD (44.1 kHz and 16 bits) vs Hi-Res audio when using wireless earbuds at the gym, in my car, or even when using noise-canceling headphones while cooking. I don't think I could even hear a difference with my 5.1 home theater system with two subs and tower fronts. If you're listening in a car, while running, with lower-quality gear or in noisy environments I think you are unlikely to hear a difference. I have, however, done single-blind tests of Hi-Res audio and lossless CD quality vs 320mp3 and I could hear a difference in a quiet environment, when I was concentrating, and using my best amp/dac/headphones. I haven't done a test between Hi-Res and CD, because the streaming service I use, Qobuz, charges the same for Hi-Res and CD quality. So I was comparing Qobuz to YouTube Music, but I imagine any differences between CD and Hi-Res would be minimal even in the best of circumstances.
2. How good does my DAC need to be so that I can’t hear the difference with a better DAC?
A) There are various opinions about what is an audibly transparent bit depth, but Amir of ASR generally says 120dB or 20 bits his his level for audible transparency. If you are listening to MP3/AAC 320 kbs or something like that you probably don't need the full 20 bits, but it's nice to know its there. Once again it depends on your listening environment (noisy vs quiet), your equipment (expensive and well tested headphones vs cheap speakers), and how much you care and want to pay attention to the music you're listening to. If you mostly have music playing in the background while your playing a video game or driving, for example, you probably won't notice the same difference you would if you're sitting in a quiet room and focusing on the music with good speakers or open-backed headphones. You can get audibly transparent DACs and AMPS (ex. the JDS Atom DAC and AMP) for around $100, so you don't have to pay a lot of money to get to that 20 bit/120 dB threshold of audible transparency. More expensive DACS aren't always about audio quality. They offer more inputs/outputs, better build quality (to show off and for better user experience), and they support more file formats (think MQA for better or worse...lol).
3. Do I even need CD quality or is 320Kbs good enough?
A) IMHO for listening in noisy or distractive environments ex. driving, exercising, multitasking, or any other distracting or noisy environment AAC/MP3 at 320 kbs is fine. If you're critically listening in a controlled environment with good equipment getting to a lossless audio file/source such as CD or FLAC at 44.1 kHz and 16 bits will be the first significant step up in quality. Going from there to Hi-Res will be a very small difference, but your mileage may vary.
Overall, I think you should ask yourself how do you plan to listen to music. If you are, in fact, like many of the people on this forum and you plan to sit in a controlled environment and listen to music I think Hi-Res music isn't very expensive and may increase your listening enjoyment. The cost difference between Lossless CD quality and Hi-Res via streaming services isn't much. If you're trying to decide between say Spotify HiFi, which is CD quality lossless or Qobuz/Tidal, which offer Hi-Res audio, think about the price difference and other features you may care about between each service. The other tradeoffs may be worth more or less to you than Hi-Res audio. If you're mostly listening on the go and whatnot I would just stick with MP3/AAC 320.
But that's all just my opinion.
Thanks!