That system can come with all sorts of configurations from the Haswell Refresh era (from a G1840 through to an i5-4690 or i7-4790).
http://www.fujitsu.com/fts/products/computing/pc/desktops/esprimo-e920-e90/
The i7 is still a great CPU in 2017 - but it all depends on price, and what you want to do with the system.
It's a small form factor (SFF), so upgrading by adding a GPU etc, is not going to be likely.
Additionally, it may use proprietary connectors so transplanting it to a new case isn't likely to be easy either.
If you want to use the system "as is", it's worth a little more than the CPU at it's core alone.
So, if it has the i7, it's worth probably ~$250 USD.
If it has the i5, it's "worth" probably $200.
If you want a gaming setup etc, then those systems are probably only "worth" the cost of the used CPU you're getting.
So the i7 ~$200, the i5 ~$150.
Anything less than the i5-4690, I'd avoid it outright.... it's just not overly viable in 2017/18.