Fletcher,
I do believe what you are asking on the "Crate" class has been done, but mostly in Elec. and I am not sure if its being done anymore.
Some of the bigger Elec. races used to run a handout motor and tires, pretty much "Spec" racing to an extent. I'd say that the last I heard of that being done was close to 10 years ago or so. I think it worked to a point, but that was in a different time in Elec. racing whereas there would be a huge difference between a "Pro" and a "Joe".
I don't run Elec. anymore, but last time I did it did seem to be a little more even than it used to. That didn't mean that some of the guys running "Pro" stock were any slower, but over all the field was fairly level.
Losi and Trinity both produced a "Spec" kit to try to keep costs down. Did it work? Maybe for a minute or two depending on the location and for what ever reason fell by the wayside.
Losi was known back then for the "Blue" tires that they included in the kits. Hard as a rock, smelled funny, and when put on the Yellow wheels lokked real ugly.
I think Hot Rod Hobbies used them once as the "Spec" tire for the Shootout they have every year.
I think part of the reason the handout tires and motors didn't last too long was the cost for the race promoter to get them and then figure that cost in to the entry fees.
That was back when a "Stock" motor didn't cost very much, 25-30 bones if not bought in bulk. That made the entry fees come in around 45 bones which was thought to be a lot. If only a big race entry fee still cost that.
I have been trying to get some of the local racers in the area to understand that concept that whlie a "Spec" or stock class sounds cost effective, the longer you run that class the more you end up spending. Its the old motor, tire, and batt. of the week club issue. Brushless/LiPo should help in that area.
Now lets see how that "spec" idea would apply to a Nitro class. It has been done and from what I remember seemed to do pretty well in onroad, but it was all done by Kyosho. I think they still run that Kyosho Cup. Tamiya has done pretty much the same thing, but with elec. Anyway, other than the rules that govern that kind of class, there can be a huge grey area that some will find a way to skirt the rules and be faster than most of the class. Its racing and many racers, "Pro" and "Joe" alike who have the know how will always find that little extra speed out of what they have. Like the Elec. mentioned above, if we go a step further and try to apply a handout motor or tire in nitro that cost of the entry fee would be so high that the "Joe's" probably could never afford to enter. Not that they didn't spend that kind of money already, but the fee alone would turn many away.
While a "Crate" class could work and I like the idea, I think it would be a hard thing to do in a nitro class. Though not impossibile to do, just harder than most people getting the event put together may wish to tackle.
I got off topic, but I hope you got the point I was after. Its in there somewhere. LOL.