I know how weird this will sound after almost 20 content updates with this aspect of the game, and that I’m quite against this current way of how Singleplayer is built at all, but let me explain.
The current base game Tour rewards are, in all honestly, extremely inadequate. Not only are they just four cars that were usually available in the Autoshows of most previous Forza games that featured them, they are also exclusively unlockable by playing the Career Mode. While it is true that there should be an incentive to at least touching the Singleplayer portion of the game, returning cars are not it. It had also been confirmed quite some time ago that some previous Tours would be added to the Builders Cup selection, but so far nothing was done in this direction. And finally, all championships in the base game Tours have 5-6 races each, while all post-launch Tours have had only 4 each for a long time now, with Open Class ones having as little as 3 races each. If the Championships can’t be shorter, then they need to be more rewarding.
For these reasons, I think the current selection of base Tour rewards needs to be replaced with other, actually new-to-Forza cars that debuted in FM. The old rewards should be put in the Showroom together with at least all currently unobtainable FM cars that appeared in Forza before FM, such as the Ferrari 488 GTB or the Alfa Romeo Giulia Sprint Stradale. On top of all this, completing these base Tours should give massive Credit rewards, upwards of 500k credits for getting a gold medal on all championships in a tour.
Here are my proposed car choices for each base tour:
Modern Tour - 2023 #96 Turner Motorsports BMW M4 GT3 + 500,000 CR
Enthusiast Tour - 1998 Nissan #23 Pennzoil NISMO Skyline GT-R + 500,000 CR
Power Tour - 1970 Ford #15 Mustang Boss 302 Trans Am + 500,000 CR
Legacy Tour - 1970 Chevron B16 + 500,000 CR
Of course, the best solution to all of this would be replacing the whole Singleplayer experience with the one from Motorsport 3 and 4, sprinkling in the car reward mechanic from 1 and 2, but this deserves its own suggestion.