Question: How much more will you pay?

[EVO-V]

aluminum radiators have plastic tops coz aluminum is expensive.. if you want to have a aluminum top, you will increase its thickness to hold the pressure.. notice that aluminum radiators have steel clips around. the drain plug will pop in case of over pressure...

aluminum is also a good heat sink compared to copper.. but copper is more sturdy than aluminum

Actually aluminum tops aren't that expensive but for it to provide as much strength as a plastic tank it needs to be thicker. Moreover, the cost of welding that is more expensive than crimping.

The drain plug is screwed on, it will not pop. You have the overflow to the reservoir to take care of overpressure. Plastic tanks pop primarilty because of clogging.

And sorry dude, but in this universe, Copper outperforms aluminum in thermal conductivity by a factor of 1.7. It is also more corrosion resistant.