While I'm not familiar enough with the full range of IQaudio products to guarantee my answer is as useful as it can be, they are designed to be hooked up to high quality pre-amps and hi-fi equipment.
Comparing as like for like as your question implies, then I would say that their products with on-board AMP (which I believe are add-ons to their DACs) are geared towards applications where the source quality of the files you play through is high, and the listening environment is free from ambient noise.
If the above match your listening conditions and material then the extra cash is likely worth it. If on the other hand, you want to listen to online radios or youtube in an office with people chatting about their business or while sawing a plank or two in your workshop then probably not.
... in other words, I think the correct answer for you is the application you want the hardware for.