Here's what I did last night:
I used Wii Backup Manager and connected my existing hard drive full of games (WBFS formatted drive). Then I connected a new, empty hard drive, formatted NTFS. What Wii Backup Manager does is create a WMFS folder on the NTFS drive and copies over all the "small sized" files directly into that folder. If you do it this way, there's no need to blow them up to full ISOs.
Mine were both 1.5TB drives, with about 800GB full. It took from about 10pm last night to 8am this morning to complete the process. The program is pretty cool--I'll be using it to keep two drives up to date in case one fails, and it automatically detects any games that are already on the drive and deselects them so you don't have to figure out where you did your last backup. Cool stuff.