For $250, you could get a new CPU AND motherboard, that would be better than the best possible CPU you can fit into your current motherboard. For example, you could get an i3-3220
and a nice H77 motherboard
for around $200. The i3-3220 is leaps and bounds better than any Core 2 Quad. As you can see from this benchmark
, the $130 i3 scores 100 points better than the $300 Core 2 Quad Q9550.