Many thanks for this fine analysis !
A while ago, I changed the screen on my Sony Vaio (vpcyb1s1e - the small one 13").
Since then, the wifi reception is very poor. I might have displaced something as the wifi antenna is behind the screen. Now I'm sure 
And I will buy a wifi usb dongle to over come this.
I'm planning to upgrade this laptop (battery change, SSD drive, RAM add,wifi dongle), do you think it's worth it ?