I can sympathise with you - losing your work is SO frustrating - but I think you'll regret going back to FCP 7 - and if you do, remember, it's obsolete - Apple will not be making any improvements and sooner or later, it will be unusable.
I certainly wouldn't go back to FCP 7 because FCP X has saved me hundreds of hours.
I have experienced the autosave failure but the 10.01 (I think) upgrade sorted id out and it has not happened on my system since.
Before you go, do yourself a favour - create a new (admin) account on your Mac and run FCP X from there. If it works, it means there's some conflict on your system (which there must be because autosave works so well for most of us).
In this case, I or somebody else can advise further - but first you need to be convinced that FCP X does work!
Andy