This may not be as much to do with how updates are affecting you as maybe some piece of software is now using more cpu cycles. The performance decrease mostly affects Intel CPU's not AMD, very little impact on AMD and typically not for average desktop usage and gaming. Look at your task manager and see what process are using the most cpu%. Make sure something isn't using more cpu than it used to. I switched back to Windows Defender (this comes with Windows 10) from the anti virus product I was using and now feel has become too bloated, and it dropped my cpu usage by about 15%. I also found that the way Windows 10 manages cores it seems to hinder performance compared to Windows 7. I found Park Control Free which has given me another 10-15% boost in cpu, more importantly it really smoothed out game play. ParkControl Free – Tweak CPU Core Parking w/o Reboots
It's easy and free to try these things to see if they help. I am like you trying to squeeze another year+ out of my am3 setup!
There are no Spectre updates except the one published by Microsoft.
Meltdown and Spectre is a general hardware bugs and all these updates is software so there is nothing u can do because bugs infect everything has a prossecor even and an ''electronic pan''.Intel have problem with both bugs but AMD only Spectre.I think this will be helpful for you.