protect OS itself from affected

All state of the art virtual machines try to seperate guest OSs from each other. If one die, other will not be affected.
But what if we has place important data in that dead guest OS? what if we has put lots of human hours to install and config this golden OS, and it has already cumulate valueable information on his long run?
For example, I install bank USB-key driver on my winXP in vmware, which is very hard to reinstall, and the outlook also record all my contact, mail, calendar,all these are very valuable. just deleting the VM will lost all these things.
So I think we still need to protect individual OS from attack, even if we has virtual machine.

On the other hand, DRAM price is so low these days,I can easiely install 6G memory to may dell desktop PC. But running all my every day program only need 512MB.
So if this means that we can sacrify 10 times of memory to exchange for security?
The tagged memory approach may seem an idea to be further refined.