Is it worth it?

Okay guys, I'd like your opinion. I'm debating on upgrading my PC. It's either I spend a little in hopes for a dramatic increase in render time or I spring for a super new awesome shiny lightening fast computer.

Currently I have a xw4400 HP workstation. Here are the specs:
Intel Core 2 Duo E6420 Processor/ 2.13 GHz, 4 MB L2, 1066 MHz FSB, Dual-Core, Intel Virtualization
4 GB (2 x 2 GB) PC2-5300E DDR2-667 Unbuffered ECC
160 GB 7200 RPM Drive (with bad sectors)
Ubuntu 12 (32-bit, by accident)

I can spend $270 and upgrade said machine with:
Intel Core 2 Duo E6700 Processor/ 2.67 GHz, 4 MB L2, 1066 MHz FSB, Dual-Core, Intel Virtualization
8 GB (4 x 2 GB) PC2-5300E DDR2-667 Unbuffered ECC
SAMSUNG 840 EVO MZ-7TE120BW 2.5" 120GB SATA III TLC Internal Solid State Drive (SSD)
Ubuntu 12 (64-bit)

They questions is, How dramatically faster would my render times be?

There will be no dramatic difference. Faster disk is a nice, but only for loading/saving... it does not effect on rendering. More ram is also nice, but it will not speed up... faster CPU does affect but again the difference is not a great as speed increase is only nominal (25%), I'd look on some quad core.

Thank you for the reply. There is an Intel® Core™2 Extreme Processor QX6800 (8M Cache, 2.93 GHz, 1066 MHz FSB) that is a available and fits my motherboard. It has four cores.

See Specs:
http://ark.intel.com/products/30720/Int ... 66-MHz-FSB

They seem to be selling on ebay for less than $75. Thoughts?

That would be a money spend well. One thing to remember as that CPU is a lot more powerful (more than 100%), you need to make sure that currently used heat sink is usable with it. Now you have a CPU with Max TDP 65 W and the QX6800 has Max TDP 130 W. So you need to have a heat sink that can handle it. If the CPU comes with heat sink, you should be fine, but it not. Try to find out on what Max TDP the currently used heat sink is made for... alternatively, just install it and do some stress testing while monitoring CPU heat.

Naturally adding a SSD and more RAM would be nice, but if you want more pure render power, you only need a faster CPU.