The whole purpose of RAID 0 is for the performance gain no matter how big or small it may be. The increase may not be significant enough to justify all the extra cost which is why people aren't using RAID 0. It's like buying to big hard drives and you're only using one. I can see how it is a waste of money there. It's not like you're combining two 120GB drives together to get 240 GB hard drive. You're still using 120GB. RAID 1 on the other hand is what people are looking for, but it's slower. You have redundancy at that point. Complete backup on everything you do. It's like a mirrior image of the other drive, but I don't think you want that either. It's common to people who own businesses or have critical data they can't afford to lose.
I think for you, it's simple just to add a single hard drive for your PC. Two hard drives get complicated anyways and performance may be small as you have mentioned.
I actually like this hard drive:
Seagate Barracuda 7200.9 SATA NCQ 3Gb/s ST3160812AS 160GB 7200 RPM 8MB Cache SATA 3.0Gb/s Hard Drive - OEM