The experience I had with the spreadsheet entries is that it is way faster for the host just to check (and maybe correct) values already entered by the player entering the challenge. Sometimes they mistype stuff, but it’s quick to fix and really quick to just check when you don’t have to type everything in as a host.
The “all the stats are revealed to everybody” issue is a real problem, yes. Another option would be to put up a spreadsheet for everybody to download and enter their values privately, sending it back to the host. Then you as the host can just copy all the columns into a single spreadsheet. This approach still does not help when you want to evalute the realism of the cars of course. Then you really need to go through all the tabs and see for yourself what has been done to the cars.
But no matter which way you choose, writing a few words for each entry seems to be a must-have for me in order to show respect to the effort the people have put into their cars. I completely agree with Chickenbiscuit here. Hosting challenges with 30+ cars is a big task and I can understand that not everybody wants to commit to that, especially given the expected fast pace of the CSR.
My recommendation is to slow down a bit - quality over quantity. A new CSR challenge in a 3-4 week period is completely fine in my opinion. This will increase the quality of submissions and put less pressure on the host.
Another option would be staggered CSRs - two parallel streams with double the time to finish a single challenge. Let’s say a new challenge every 2 weeks with 4 weeks to finish each challenge (2 weeks for submissions, 2 weeks for reviews). Then players have a new challenge every 2 weeks, while the host has 2 weeks to finish a challenge. Or make it 3 streams - 1 week for submission (this hopefully reduces the number of entries) and 2 weeks for review.