I have my doubt about if high density resin would actually even get hot enough to the touch.
Well okay. Which part of the laws of thermodynamics don't you understand? The fans would need cleaning if they didn't have a filter behind them (intake fans).
Then you'd just have to clean the filters instead. 2.5 inch HDDs are dissipating less and less heat as they evolve.
No they don't. My laptop drive gets much hotter than the HDD I had in my A1200. Why? a) It's spinning faster.
b) It has a higher density, which in turn means that the heads need to be closer to the cylinder.
Power supply get stricter regulations, such as 80 Plus, which dissipate less heat and give more wattage output.
Besides the point that 80 Plus isn't a regulation, it is not possible for any PSU to have an 100% efficiency rate. Some heat will always be generated. Now while it's true that modern PSUs are marginally more efficient at transforming electricity, they need to generate significantly more power. So yes, a 20 Watt 2007 PSU will waste less energy in the form of heat than a similar 2004 model, 20 watts is no longer sufficient to power even the most basic "Vista Ready" PC. If we say that a 2004 has a 95% efficiency rating at 20 watts, it will be wasting roughly 1 watt of heat. A 2007 with a 98% efficiency rating, pumping out 400 watts of electricity will still be wasting 8 times as much heat. CPUs such as the new INTEL core 2 Duo and Quad dissipate little heat compared to the old Pentium 4s.
Which was a flaw of the old Pentium 4's, more than anything. Seriously, which heatsink is larger, the Intel Core Duo one, or the one you had in your 2004 PC? The only ennemy towards a dense system remain the graphics cards
No. Even without a graphics card, or using one of the Intel on-board ones Gabriel mentions, the biggest enemy is the obstruction of airflow. The denser your system gets, the more difficult it becomes to dissipate heat, because of the lack of sufficient airflow, around large surfaces (like for instance a heatsink). I'll conclude from what I read here, nobody seems interested in the concept, or are afraid to voice themselves.
Or maybe they just realize that you're wrong?