I upgraded an old Thinkpad with a faster CPU to use on my boat. The howtos on the Thinkpad forum were very helpful and I learned a great deal about laptops, mostly how cramped it is in there, but the upgrade was only marginally beneficial. I was starting from a very slow CPU to one that although 60% faster still didn't make a lot of difference. My conclusion was to make any great improvement, you need to have a new motherboard to take a more up to date CPU, more RAM and a bios that accepts an up to date (now) SATA drive. There is no way you or I can make a new motherboard to fit in the space available so you would have to buy it if such a beast was available. So a new laptop is the answer. Linux would extend the existing hardware's life a bit (I would chose LinuxMint), but what you would use the laptop for, would decide if any of these changes was worth doing. Interesting though!
Tony