FatBelly, you got a 30-hour Tivo for the price of a 14-hour Tivo ($300), you are still entitled to the $100 Tivo rebate with service activation, netting you a 30-hour Tivo for $200. I'd say keep it.
OTOH, if you plan to hack your Tivo, I'd say keep the 14-hour unit. Rebate it as best you can (to $0 or $100, whatever you can get). The new hard drives and bracket will run you about $275, but when you're done you'll have a 90+ hour Tivo for $275-375. (Of course, there's labor and skill involved, and you do void your warranty by doing this.)
It's your call.
Steve