Is value RAM really worth the savings?

Value RAM has slightly more relaxed timings, which on a Core2 proc is not an issue. Had you wanted it for an AM2, I'd advised against it.

Nothing wrong with value ram. I have it in one of my rigs and I have some high end ram in my other. I don't think the real world benifits of performance ram is worth the extra cost

If you don't plan on OC'ing, get value ram.

The only reason I bought performance for my rig is to toy around with overclocking. It was just out of curiosity.

If you intend to get the most out of your overclock, it is better to go for better RAM. But if you are satisfied with a slightly lower overclock, valueRAM is just fine. Either way, C2D CPU's are turning out to be great overclockers and I don't think you are going to need that extra few MHz to get great performance.

Keep in mind that C2D (from what I've heard) performs best at a 1:1 memory ratio, so if you are looking for your FSB going over 333, you may want to go for DDR2 800 so you have that extra headroom to known stable 400 FSB.

Simply put, DDR2 667 performance RAM with tighter timings may overclock higher (to DDR2 800 speeds maybe), but DDR2 800 value RAM with looser timings will run at it's rated speed. (Or lower, obviously)

Value RAM is ok if you don't OC. However, there is a huge difference between performance RAM and value RAM in terms of overclocking. Performance RAM has heatspreaders and memory chips are carefully selected and tested.
Frankly, I recommend performance RAM. Here you can find a review (seven of the greatest RAM manufacturers) :
http://www.driverheaven.net/reviews/PC2-6400%207-way%20memory%20round-up/index.htm