I see nothing wrong with the CX750M PSU [0]. What do you consider good guts? Compared to the macbook charger, which gets fairly hot under load, I see it as more capable.
2. Cooler cost has very little to do with performance. Thermalright units compete with liquid coolers for a fraction of the cost[1].
3. What does a macbook case offer? Holes for ports and the keyboard, hinge for the LCD. The components themselves do the work. What does a ~$50 case [2] not do? Plenty of cooling, mounts all your components.
4. For llama.cpp text generation, an M3 pro does ~31 tokens per sec with the Q4_0 profile[3]. A 3070 does ~34 tokens per second [4].
WRT the motherboard, I'm not sure what did I suggest upgrading? I recommended cheaper parts than the original post.