Normally only for show. They can look OK but old father time isn't kind to the materials. It does make the survivors very rare and are priced accordingly.
What would be winner, winner, chicken dinner is if somebody made new ones with modern fibres and clear plastic whatever it is. I think they would be stronger, than the originals, and there would be a market for them because they are iconic and look cool. It wouldn't affect prices on originals as collectors will still want them. Black wheel covers like EZ Gains time trial things with the Disc Drive pattern and logo printed on them might also be sellable.
...and no, i am not that somebody because i don't have the lolly. If i did, though, i think i would try. I see someone here in RB in 2014 had a go at covers and i found these