Really short? Oh, so you aren't going to play ever again if you get 100%. So this game has no replay value at all? I guess they should remove the arcade mode and online play from your copy. This isn't a FPS, there is no "end".
GT5 is NOT really a brand new game, really just an update. Why shouldn't you be able to "continue"? Heck, some cars and tracks are exactly the same! Seems like your cars and or money should be easy to transfer. Imagine if F1 and NASCAR teams started every year with 20k and had to get by on their winnings, right I can see that.
Yes, there is an adapter. I have played GT4 on my PS3 and transfered my game save to the hard drive.