I feel Geekbench scores are a little misleading when comparing the cMP with more recent systems. A cMP is competitive in situations when it is configured with more cores than the reference system and only when running software which can utilize those additional cores. Currently four cores is the upper limit for the majority of applications making the Mini and iMac a more suitable choice for the vast majority of people (all else being equal).
As to the purchase of this system I would recommend the OP consider it but for reasons other than raw CPU performance. It's a quad core, 2.8GHz system which means its multi-core benchmarks aren't going to overcome its aging architecture no matter what software the OP plans to use on it. The ability to upgrade it (including processor upgrades), and expand it are solid reasons to buy it. 24/7 operation and "cool" factors are other possible reasons. Raw CPU performance is not.
I say this as an owner of the exact same system (except mine has 32GB of RAM and acts as a VM host platform).