I really don't see the sense behind mods.
1. Mods don't make sense, if you need more credits:
If you need cash, all the winner credits are close to nothing compared to the spin wins. You may get 20,000Cr from a race and you may have to do 2 races to level up again, but even if you just count the top prize of the level-up spin, that's on average definitively higher than 1,000,000Cr, but let's say it's 1,000,000 with a winning probability of p=1/9th,
that's 111,111Cr on the average level up, if there was only the jackpot. Yes, maybe it's a car that you don't want, but you can sell cars again at 50% but if you keep it and by accident win it again, you win 100% of its value in credits.
[By the way this also devaluates the VIP-bonus compared to previous games, but personally I don't care, I'm not VIP because of more in game cash]
2. Mods don't make sense as a difficulty adjustment:
If you need more grip, buy better tyres or another handling upgrade. Should that get you over the pp-limit of your race, then you shouldn't
have it... just like the grip-mod. If you need to make the race easier, adjust the assists or drivatar difficulty!
3. Mods screw the leaderboards:
If a friend in FM5 had a 4s better lap time than me, but his time was invalid, I could assume that if he tried really hard, he could get a valid time that was 4 seconds faster than mine (admittedly just "assume" because he could have just cut the track). Now all invalid times are more or less
meaningless. Maybe that's why the used car's pp isn't shown in the leaderboards anymore (at least not shown directly, you can still look it up on the right, if you go to a specific gamertag on the leaderboard).
The only thing where I see a field of application for mods is for simulating/roleplaying minor team differences in racing leagues where all the cars are basically the same, but then the AI should be able to apply team mods too.