I'll use my case, but I think there is a lot of people in this situation.
My Mac Mini is 2007, 1.83GHz and now with 3GB of RAM and a Kingston SSD, running Lion. This combination provides satisfaction when working with web design, some publishing and daily taks. However, Safari is getting old and everything that uses graphics, specially 3D acceleration, is a problem.
Reading some articles around the web, it seams the only way out is to try the PCI port through Ethernet adaptor. In theory, might be possible to adapt a PCI connector (PCIe?) and connect external graphic card. In the real world, looking at my logic board, I don't think it's possible!
But recently I've seen some external cases for graphic cards that uses Thunderbolt port. So my new idea is to use the SATA port, a SATA-Thunderbolt adaptation (already exists) and a graphic card enclosure. This is not to get powerful graphics because the 1.5 GHz of Mac's SATA port will limit, but at list I'll be able to install newer OS with a simple hack, and newer graphic drivers.
What do you think about? Ideas?