If there's no problems with your PC as it is, then my advice is not to bother with a BIOS upgrade. Bios upgrades when they go wrong can result in a completely dead/un-useable motherboard.
My motto - "If it aint broke, don't fix it."
A new Bios version may allow the motherboard to detect and use newer CPUs (so, maybe needed if you upgrade the CPU in the future) and there's a small chance that a newer bios might enable other features or increase performance slightly.
EDIT: It wasn't SiSoft SANDRA that recommended you update the Bios was it ? If so, then definitely ignore it .. it always says that