2006 MacPro - Worth upgrading for use as a VM host? I have a MacPro 1,1 bought in early 2007. Earlier this year I was about to recycle it but tried installing an SSD as a boot/apps drive. It has been a great success, it now feels like a new machine and I'm contemplating souping it up to  16GB of RAM and using it to run Windows VMs (I'm a .Net developer) in Parallels Desktop or VMWare or similar.

The RAM is going to cost &lt; $50. I was wondering if this is a good idea in 2014 or if I'm going to hit a load of constraints imposed by the age of the hardware. Any comments or observations very gratefully received. I cannot and will not pay thousands for a new MacPro.
Short answer, yes.

The MacPro 1,1 can run 10.7.5 as it's latest OS.  I have a 2008 Black MacBook which runs the same.  Despite being on an OS from 2011, you can still run the latest version (v7.1.0) of VMWare Fusion.  You can also jam 32 GB of RAM in there.  Plus, the Xeon from 2006 will almost be comparable to a Core i5 from a couple of years ago.

Like you, I also updated to an SSD.  Even though the RAM in my MacBook is only 2 GB, it is an amazingly fast machine considering it's specs.  SSDs are simply amazing, they are the best upgrades you can make.

I also have a 2012 Mac Mini.  I installed the maximum 16GB of RAM and a 240 GB SSD.  I am able to run OS X as well as a Windows VM and 2 Linux VMs with almost no degrdation in performance.

It's worth noting 10.7.5 might soon be cut off from receiving security updates, however I imagine you can configure some networking where the VMs have internet access yet the host machine only has access to the local LAN.

I'd say go for it.  That machine is far from dead, there are still some amazing things you can do with it.