but also far less powerful than mine.
Depending on the age, it may actually be pretty close to the power of your machine, just without the expandability. I was quite impressed with the capabilities of the one I had at my last job. Handled running 2-3 OSes at the same time just fine, once I filled the 4 memory expansion slots.
The somewhat recent push for much more power efficient processors has been great to see. Intel is now focused on introducing their new tech first in their mobile processors, then desktop, then server. It used to be the other way around, with the server chips eventually being chopped down and hobbled to work in a laptop.
There are lots of punters out there who upgrade to the latest and greatest every 2-3 years, so just grab their cast-offs for 1/10 the new cost.

Hey now, some of us like new shiny things

I do wish at times I could reclaim some of the cost of my machines, but they tend to turn into hand me downs for the family. My grandfather is running the Mini I bought in 2006, and my grandmother has the laptop from that year. My desktop was new in early 2008, and the current Mini is actually a tradeup. My last company needed an older Mac for QA testing, so I traded a late 2008 model for a 2010 version.