How to display car show flat plaques without covering wall in nails?

How about multiple shelves? Less holes and you can lean the awards against the wall and add decorative items like small potted plants, auto books, and even model cars to tie into the awards.

3M Command hooks. Just stick the on the wall.

I saw a pic of some design where the designer put up a curtain rail on the wall,minimal holes, and hung pictures from it using a chain for each one. It was very effective and looked nice. You could use whatever you wanted to hang your stuff, cord,rope, etc. and as the plaques don't look large you could have more than one rail so it's like a display wall.

Make a statement piece from them, especially since you have so many plaques. Cover a piece of mdf large enough to hang all the plaques on (if there are too many, you may need more boards) in paint or road maps or wallpaper in a theme matching the awards. Add simple mouldings around edges to frame. Hang as many plaques as you can on the board. You can use silicon to adhere them. A larger 'picture' is nicer than a lot of little plaques stuck on a wall. Use a couple of 'French cleats' to hang the larger mdf board Check the picture hanging section of Walmart for these. Or have French cleats made of wood. (Google the directions) You could also add small shelves to the board for stand up awards, but definitely silicon them to the shelf.

Don't the plaques have a strong adhesive on the back (to stick them on the car's dash)? Thats how they are in this part of the country. If so, your should be able to arrange them directly on the wall.

Perhaps get or create a large shadowbox type frame for favorite car pics and place plaques , awards etc on 'shadowbox shelves' surrounding pics