There is a copper base plate, but it is connected to the aluminum heat sink by a layer of thermal compound, without any mechanical binding, this defeated the purpose of that material
Are those heat-sinks fairly "standard" ? Is it possible to buy higher quality replacements that might work in the SP20's ?
its possible, but not even remotely worth it.
16x heatsinks = $25 if you get a bargain
time spent opening a case, melting the glue holding down the curent heatsinks = 1hr, voided warrenty, likely at least 1 cracked or snapped component
time spend properly cleaning, pasting, and applying a new heatsink to the chips then re-assembling = 2hrs
if you are lucky and do it all properly, you will either be able to reduce fans at full speed by 10-15%, or otherwise perhaps push the unit to 1800/1350W at the most extreme. Thats about a gain of 100GH/150W for the cost of 3hrs + $25. For reference, $25 put towards the cost of a new $400 SP20 would be effectively worth 150GH/100W
if you're unlucky you will re-assemble the device and find that multiple chips no longer read due to various errors (you cracked the asic, nicked a resistor, w/e), and effectively lose a large amount of your device functionality
its not worth a mod