without knowing what motherboard you are using, its hard to determine what possible upgrade paths you have ahead of you for the processor. But I would point out that the Phenom X4 series never really lived up to expectations and even the budget chips of today offer more performance. Chips like the $90-100 Athlon II X4 series, or the midrange Phenom II X4 series that start at about $140. Actually newegg even has a Phenom II X4 940 Black for $117
which is en exceptional chip, and easily overclockable thanks to the unlocked multiplier.
but of course all that depends on whether or not your board can accept any of these newer chips.
In terms of every day performance you have plenty of ram, in fact more than you really need. But you will be held back by the cpu, most of the day to day stuff you will be doing will not be multithreaded so you will really only be using a single 2.3ghz core. And the story is the same with gaming, though a few games these days can use all 4 cores (or more), you are still limited by the architecture of these early phenom chips. Lower resolutions tend to be more cpu bound, and with a 9500 GT i doubt you are really playing at a high resolution such as 1680x1050 or 1920x1080, where the games are more gpu limited.
But knowing what games you play and what resolution your monitor is capable of would help us make some suggestions, but if you did want to do a good upgrade on a reasonable budget, you could do it for $200-$250 and stand to gain significant performance. Something like that Phenom II above (or a Athlon II x4 635/640) along with an ATi Radeon HD 5750, and you'll be golden.
I would also start thinking about moving away from vista and towards windows 7. It is much leaner and more capable of handling available resources so its a much better platform.