Other than finally starting to move to higher core counts, going from gen2 I series processors to gen8 I series really isn't much of an upgrade. I personally am curious what is wrong with your laptop? In reality, I would just upgrade it from 4 gb ram to 8gb ram and call it a day. If the HDD needs replaced, then I would do that also.
I'm not super geeky with things but from what i gather, i would get that blue screen of death randomly during idle. It can blue screen in a matter of 5 minutes or after 5 hours. I've reformatted the samsung 850evo 500gb that i have and it still has the problem. My techy people is saying bad sector in the drive or bad solders on the board. I took the whole thing apart and cleaned it, looking for bulging capacitors and didn't find any. I dont know how to test anything else.
Its was a laptop from 2011 that i paid like $500 for, it has served its purpose. The little things like battery life and poor wifi signal i was able to deal with but to me i think its time for a newer garage laptop. I would love a XPS13 but that is extremely overkill for a DIY garage laptop. 8gb DDR would run me about $50, another SSD would run $50-100, a ebay battery could be $50. So thats $200 and it still might not fix my problem and i still have a 13xx resolution, below average wifi card and no USB 3.0.
I've been looking at the thinkpad x240 on that arrow website linked above. Looks good except for the resolution, $300. It does come with window 10, so i might have revert back to win7. Reviews say it should be a 6-9 hour battery life because it as a internal 3 cell and external 3cell(or higher)
i found them on ebay too, this exact one is the one i'm thinking of buying. The lack of HDMI port is the thing i'm looking to get a workaround on.