I tend to use a sliding scale between aesthetics and functionality for something I want a replica of.
Stuff like wallets, toys, belts, fall very much towards the aesthetic end of the scale. I'm more than happy to buy a rep wallet, or toy for example , because I find them plenty sturdy enough for day to day use. Stuff like bags/trainers (for day to day wear, not sports use)/watches fall somewhere in the middle - you need some element of function from them, and so need to find an item where at least some effort has been put into making it fit for purpose. I wouldn't expect a replica bag or trainer to take the same beating as a 'well made' one, which has gone through (allegedly) a more vigorous quality control process, and I would treat them accordingly.
For me speakers and headphones fall at the complete opposite end of the scale. Although they obviously can have a 'design' element, for me the joy in their use lies in their function, not their appearance - and this is unquestionably where replica products fall flat - and where money is saved. While I can get 90% (to put a number on it) of the joy from a rep watch that costs 5% of the price of the gen, the same simply isn't true with headphones (in my experience). If something is expensive based on it's function, and I need or desire that level of function, I'd rather front for a real one.
Obviously different strokes for different folks, but thats my 2c worth!
Totally agree with this.