You´re partially right. In the beginning the wheel spin was far more generous and we could see 400k cars and horizon edition cars much frequently. Now after the horizon editions renewal, the wheelspin is very bad.
So partially you´re kinda out of luck because you didnt have it 1st, and now you´re unlucky again because they made it worse.
I´m not level 300 yet, and I got all horizon cars released so far. I´d say 70% from lucky draws, and 30% from lucky biddings on auction house (i got a lambo countach for about 224.000 when in the same minute where people were giving 800k bids.
I tried to quit and reload the game when I see that the prize is a crap… doesnt matter, the result seems to be set right in the beginning of the process, then the game starts the slot machine animation, and you see the result. Some animations are wrong and mysteriously the roulette spins a bit more to give you 2000 or that crappy car that nobody wants.
Also it looks like there´s a tendency to give better or normal items. Some spins animation look precise on giving the horizon cars, while others just feel like normal. For people for bought the standard edition the spins are like “mmmmmm”… But for people who bought the deluxe or the top expensive version, the spins seem to be HELLOWWW YOU AGAIN, lets see what we can get 
I got no proof to support this, but it feels like… so have your own conclusions.
My advice is: get the perk that allows you to buy a spin for 50k, then DONT ABUSE IT !!! If the prize isnt what you looked for, but the spin gave you something like 35k, pay for another spin (total lost 15k so far, since you paid 50k). If you got another 35k give it another spin (so far you lost 30k, which is manageable), If you got less than 40k, QUIT (at this moment you´re losing 50k for 4 attempts, which is tolerable), but if you got 40 then pay for another spin (you lost 50k now), and still if the prize isnt what you expected, quit if you didnt get 100k.
It´s all about credits… stupid cheap cars dont count. If you´re feeling you´re not going anywhere, use the perks to give you extra money and exp on championship and the next 3 campaign races (mind these 2 perks), and get money to go to auction house, and try your luck there. The cars will cost around 400 to 700k, thats the rational limit you can push yourself. If someone else is biddind more than 700k on a horizon edition, let the crazy one spend his money and forget about it.
Now that I have all horizon cars, I just use the BAC MONO, the BMW M4 and the M3 (for drifts). Also the old mustang helped me once, and the rest is dusting. Try to focus on the cars you need, and you´ll surely suffer less 
I wanted to have all horizon cars and I got them all (so far 25 october), but now im not using almost none, and I ended up with 1.2 million left. Was it worth it? You decide.
PS.: the deals I´m proud of were the ZONDA for 1.150.000 (more than 1 million in “discount”), the La Ferrari for 900k (600k saved), and the Lambo countach for 224k.