I'm not in a rush either, but I'd also like to play other games, and ideally, not grind the same few races.
I came into GT7 with the promise of a car collecting game, fully wanting to collect (and drive) every car in it. All of that driving of each car, I expected to earn me enough money to buy more cars. Instead, custom races won't pay enough, and there's not many career races, so grinding the few well-paying career races is the only way to truly Catch 'Em All... outside of MTX. Honestly, that's not fun, and it goes against my desire to collect and drive lots of cars, which seems to be the same desire you have.
So my question to you is this:
How will you truly afford all of those cars that you want to collect? Will you grind Fishermans? Will you do so many custom races that you make the money anyway, no matter how slow? Will you just do the career races, regardless of how much they pay? Have you figured something out that I haven't?
None of those are fun options to me. For me, it could be solved by simply adding more career races and paying more for custom races. That's all it would take for me to be happy with this car collecting game's balancing.