Laura,
Normally if the ASA is running fine (no problems) it is not recommended to upgrade.
In case you require an additional feature or functionality incorporated in versions 8.2 or 8.3, then obviously you should upgrade.
But, 8.0(5) is very stable and if there are no problems, I will suggest to stay with it.
Keep in mind that 8.3 consumes a lot more of memory.
Federico.
