For a normal event, no. The way Circuit Experience is, it makes sense to be gifted the car being used.
I'm not too sure about that, especially if they go with Gr.4/Gr.3/Gr.2/Gr.1 cars like in GT Sport's version of the event. If they decide to do that again, I'd reward cars that might have something to do with the course itself, such as its location, or a car that may be appropriate for the layout. So I might reward a Gr.3 car for Dragon Trail Seaside, and perhaps a Jaguar E-Type for Goodwood Circuit.
But if they go for a truly wide variety of cars - in the N-Series, the major groups, and Gr.X - then I think that would be a scenario where rewarding the car you drove would be more appropriate.
EDIT: Given that there does seem to be a larger emphasis on the world map in that initial reveal trailer for GT7, maybe the circuit experience mode could be divided into regions, where each region is similar to a license. So there would be three prize cars per region, as you'd be rewarded one for getting all bronzes, silvers, and golds. There'll likely be three regions: North/South America, EMEA, and Asia/Oceania. And much like the license tests in previous games, the prize cars could be from a radical variety of groups and classes.
EDIT2: Just using the GT Sport car list alone, here would be my picks for the three prize cars of each region, plus a hypothetical diamond reward:
Americas: Ford Mustang GT (2015), Dodge Viper Gr.4, Chevrolet Corvette C2, Fittipaldi EF7 VGT by Pininfarina
EMEA: Alfa Romeo 4C Launch Edition, Porsche Cayman GT4 Clubsport, Jaguar E-Type, Alpine VGT Race Mode
Asia/Oceania: Nissan Fairlady Z (Z33), Hyundai Genesis Gr.4, Toyota 2000GT, Lexus LF-LC VGT
EDIT3: As another alternative, there could be a large emphasis on the circuit experience prize cars having to do with a location, such as how the "F" in the Lexus RCF stands for "Fuji," or how the "N" part of the Hyundai "N" has to do with both the Nurburgring and the Namyang test center in South Korea. But I really like the idea of the circuit experience being divided into regions, and instead of there being a single prize car for each course, there could be multiple prize cars for each region.
EDIT4: I just think that, if you're loaned various Gr.4/Gr.3/Gr.2/Gr.1 cars for each circuit and then you win those same cars, then being given free race cars would diminish the pacing of the campaign. Especially for the latter two groups. Otherwise, I really liked the circuit experience in GT Sport, and I hope it returns in GT7.
I actually can't believe that never registered in the brain as many time I watched the trailer, damn.
I really hope its something similar to what
@SuperKlonoaGT suggested. Paint chips and rims would be what I would prefer. Getting reward cars for free by simply doing a lap around the Nurburgring takes away so much satisfaction away from the car collecting process, and just bloats my garage with a bunch of useless Gr.3 and Gr.4 cars I have no interest in ever using. It was fine in GT Sport, having it in GT7's GT Mode would be a massive, massive mistake. It would singlehandedly ruin the singleplayer progression of the game.
Keep in mind that the initial reveal trailer could very well be from a much earlier build of GT7, and game development (from the little that I know) is very volatile. Tons of stuff can get added or scrapped at various points of development. I don't really want paint chips or rims, and I definitely agree that prize cars wouldn't be ideal, either. I think a simple credit or mileage point prize would be ideal, with said prize increasing for each subsequent day - or there could be a bonus if you complete your daily workout for a whole week, and/or a month, etc. like how in Pokemon GO, there are the Research Breakthroughs you can collect for every seven (consecutive or not) days you complete a research task.