I badly neeed to upgrade my computer, but the problem is that I can't afford a full upgrade at present. LR updates thumbnails slowly, AE renders slowly and LRTimelapse takes forever to build visual previews... (I'm working on an i7-2600 3.4 Ghz CPU, Asus something motherboard, 16 Gb RAM, NVidia GeForce GTX 560 graphics card, Win 10 - all bought in 2010, if I remember correctly). 

What I have in mind is to build a work drive/volume by installing a raid adapter and a handfull of drives and run it as Raid 1. That should boost things up a bit. I'm also thinking about getting a new graphics card, mainly to solve issues with LR and AE. 

Any thoughts, will it boost performance as described? 
Which graphics card would you recommend?

Any input will be highly appreciated!

First: Lightroom thumbnails are not important, don't wait for them, you don't need them!

The cheapest and by far most efficient option would be to get a decent and large SSD and work on that. Best would be 2 SSDs - one for the W10 system and one as your working drive. Forget a Hardrive-Raid.