But the silliest thing is...
After you have a second PSP, you don't need so much money.
If you turn autosave off, you can buy all the shareable cars you want, and give them for free to your second game. You should now save the second game. (But make sure you don't save your first game!) Now, restart the first game (use "Home" key). Now have the second game share its garage with the first game! You only need as much money as allows you to easily buy all available shareable cars each day--and even that's not a necessity (you could do a couple of "batches"). With shareable cars, the game even takes care of determining which cars you don't have. You do need some extra money for tradeable cars, however.
Now, if you have extra memory sticks, you can do a similar thing with "Trade", but you need to plan ahead a little--snap up those cheap tradeable cars (e.g. Citroën 2CV's or Mazda 323F's) in bulk (in both first and second game)! You can trade them to your other game for expensive tradeable cars. You can make a save, buy the tradeable cars, have your second game give you a cheap car for them (note that trading does do an autosave, though), and then go back to your backup memory stick. You can then get your cars back for Cr21,000 2CV's. Another extra memory stick is necessary if you also want your second game to keep the expensive cars. So you end up buying expensive Tradeable cars for the cost of the cheap cars. (It does seem silly that you can buy up to 10 copies in each colour of the "rare" tradeable cars).
Quite honestly, though, although the "shareable" technique is really easy, the "tradeable" technique is quite time-consuming and stressful.
I'm glad my PSP's are two different colours (black and silver). If yours are both the same colour; you might want to very clearly mark them somehow. (at the very least, use different utility screen backgrounds!)
The difference in AI in my second game is noticeable. It couldn't beat a 787B with an R92CP at the 'Ring (S versus D). I needed to have my first game autopilot use a Lister Storm to allow the second game R92CP to win. When you add extra AI players, you seem to get a slightly less good clone of each player's car. Unless it's actually my tuning.
Of course, maybe I should try and spend more time practicing driving the more powerful cars myself.
I tried to copy my game progress file to the 2nd PSP (with its own memory card), but the game (GT) does not except this and complains that the progress data came from another system (my original PSP).
So my question is, is there a way to transfer/copy the game progress file to another system, without having to resort to major hacking?
I've heard from a couple of people the answer is "no". Which would be annoying if a system dies.