These things have amazing build quality. I bought an 8-core 2008 Mac Pro in 2008, and it's still running 11 years later. I've added SSD's, better video card, and it worked great until apple dropped support for it. In 2008, it was a good value compared to other professional workstations for getting 8 Xeons and 32GB of RAM. Sadly, you can't even install later OSX versions on it because those require AES-NI and AVX instruction,s which these CPU's lack.
My G5 Mac Pro tower was my first Mac, and a rock-solid piece of kit, which I would occasionally open just because I could.