Whether it is worth it or not depends on you and your intended usage. But, in general, if it is an octa-core (dual cpu), then yes, could very well be. iirc, the Xeons used in the 2009 models where already two years old at the time, but, Xeons are essentially i7s with a few tweaks (Xeon: support for ECC RAM, way more L3 cache--which makes them fast(er), no onboard video, cannot be over-clocked, way better with multiple threads and virtual cores, a few others. i7: onboard video, can be over-clocked, way faster with single threads).
If it's a quad-core (single CPU), then I dunno, however combined with 48G RAM, a 30" ACD, 1TB SSD, and assuming you can successfully flash it to 5,1, and factoring in $150 in shipping costs if purchased off eBay, $900 is not too expensive.
I don't if there is much difference between the 2009 Mac Pros and the 2010 Mac Pros but the only difference between the 2012 Mac Pro and the 2010 Mac Pro is a slight increase in speed and some say that the 2012 Mac Pro is essentially just a repackaged 2009 Mac Pro with the speed bump. That being said, the 2012 Mac Pro (12-core) still blows away pretty much all currently offered Macs in their base configs.
To answer questions:
1. Yes, you can add USB 3.0 via PCI card. Will certainly be faster than USB 2.0 ports, but likely still a little slower than native 3.0 support.
2. Pull the lever on the back panel to release the side panel, pull out the "box".
3. Haven't used a CD or DVD in a long-time, but pressing F12 should do it.
4. For a longer life span, maybe. the 2010 - 2012 Mac Pros will be supported with the upcoming High Sierra and considering that HS will run on iMacs and MacBooks going back to late 2009 models, I have a feeling that the the 2010 - 2012 Mac Pros will also still be supported with macOS 10.14.
5. Depends on usage, but... ...the "cheese grater" Mac Pros have a cult following that's likely not to change anytime soon. As these become rarer, the case alone could fetch $200 or more in a few years and their will always be at least one hipster willing to pay $$ for a vintage 30" ACD.
08-17-2017 01:53 PM
Would have to agree with @bamf-hacker, I personally wouldn't pay $900 for a Mac Pro thats 8 year old. While it may have ludicrous amount of RAM and a very large SSD, the GPU is still 8 years old. So i personally would spend a couple extra bucks and pick up a 21.5" iMac from 2015 on sale somewhere and upgrade the HDD to a SSD
but with all that being said, if you really want it and you love it, then its well worth the price of smiling everyday while using it 
