As with panzer06's thoughts, the sensor issue with the 2010 model troubles me. I can't speak for the SSD but with hard drives, from what I have been reading latterly, there is more at work than making sure you have the right sensor cable designed for the specific model of drive; that cable apparently won't work properly without the Apple firmware on the hard drive, something not talked about by third party sellers of hard drives, I found. There is a long thread about the sensor issue on OWC's blog. There are several suggested workarounds, including using a glue-on sensor from a previous generation iMac but even then people are arguing over that and other workarounds.
That aside, having watched a few deconstruction videos and winced at a couple of people fumbling around to remove the panel's relatively fragile ribbon cables, I would think twice about potentially doing damage and voiding your warranty. If you have a definite need and you live in the US, perhaps consider OWC's fitting service, their SSD drives review very well, though do read their somewhat ambiguous small print over whether their service voids your warranty with Apple or not.
At least upgrading the memory is straight forward, with the caveat that the 2010 model apparently works with 16GB without random shutdowns if you use Samsung memory; a few have said Hynix works without problems too but most stories relate to Samsung working. I couldn't find a British vendor who could guarantee the memory their depot sends would be Samsung, so will probably order through OWC.
