Barden seemed to say specifically the game would be better if money was harder to come by. But I think it's good when a game has a natural "easy mode" and "hard mode" (and variations in-between). In my current GT2 game, I want to end up with a garage full of cars capable of entering and winning all events, including Manufacturer's Events. You need 88 cars for the 90 manufacturer's events, so that leaves only 11 more (want to have room for a prize car) available for events which those cars can't win. I do want all entrants to meet the stated entry requirements (using a car seen in previews is one approach), so my choice of cars may become tricky towards the end.
However, I don't want to have trouble financing this, so I simply allow myself to use the Red Rock Valley Cash Machine whenever I need it (not sure which car will be left in the garage at the end for that purpose...).
In fact, when I did try to finish GT2 in "natural career order", I found money very hard-to-come-by, and I found it uninteresting after a while, and I actually stopped.
So it's nice for the game to allow players to pick their own rules, to some degree.
Now the AI opponent difficulty... The rubber-band algorithm is so severe in this game that it's frustrating in both ways at times. The other night I entered the Turbo race at SSR5 with a Skyline with no extra turbo fitted. The AI somehow let me to the front for the first lap, and then just scooted by on the straights after that. But, in general, it seems if you've picked a fair race you should finish with a pack of cars less than a second behind, and, if you manage to open up any more of a gap than that you're probably to some degree "cheating" (overpowering the field). Which, while it means if you don't overpower the field you need to be very careful in order to stay ahead, also seems to mean that if you give yourself only a slight advantage (equal cars might be a slight advantage?), you can't gradually build up a lead by good and careful driving. And at some tracks everything is even more confused by the very bad AI course knowledge, e.g. they like to have spontaneous one-car accidents at the first two corners at Apricot Hill and the first uphill run at Trial Mountain.