Good cards is going to have its own RAM, if it doesn't have its own RAM then its no better than your onboard RAID. Good cards are expensive.
Personally I don't think buying a good card is worthwhile unless you are doing RAID 5.
Don't worry to much about onboard RAID horror stories, they mostly deal with RAID 0.
If you are concerned I would play arround with the array. Pull a single drive out and connect it to another PC and see if it has any problems reading it as a single drive. Start with one drive disconnected and then practice recreating the array without reinitializing it (initializing = erasing). Simulate a drive failure and rebuild the array from the existing drive. See what it takes for you to actually lose data.
My (limitted) experience with 2 drive RAID 1 arrays has been that the worse case senario is that you are left with 2 working drives each a complete copy of all your data which you can readily convert back to a RAID 1 array without data loss.