Do we have to be worried about Spectre and Meltdown being used for a large scale attack like Wannacry? Even though the patches coming out are being deployed to a most recent systems, there will inevitably be A LOT of systems that won't be patched.
The affected systems range from routers to smartphones to data center servers, not all of them will be updated. If there is a way for meltdown to be abused and chained into anything else that could escalate privileges or other any other attack types, it could be used to hit entire networks if you have even a few unpatched devices.
Being able to snoop kernel memory seems like a huge problem and even if most things get patched, it seems like even a few unpatched systems could compromise everything else on your network. Sounds like this problem is only going to get worse and the performance degrading patches won't be the worst of it.