I'm doing a rebuild and currently have a single WD3200AAKS (single platter) for my OS. I was wondering if I should add another in raid 0 or get a newer faster drive? No SSD, can't afford it.
I wouldn't bother unless you need the space. I've had too many headaches with raid. If one drive starts to slow down, the entire thing will either crash or run with errors. I tried running and it always failed after several months. My brothers ran the longest, ~ 1 year before one of the drives slowed down and crashed his system.
Personally I would run with the current hdd until I could afford an SSD...which is what I am doing now.