I have had lots of cars and lots of wheels, some with spigot rings and some without, including mud tyres on 4x4's and proper race cars , i have never had a problem when not running them, on vehicles with tapered seat or concave seat wheels correctly fitted and torqued.
you dont need to mount anything "by eye" as you torque the nuts up in sequence the wheel will centralise itself.
i have had a problem with plastic ones getting stuck on the hub due to it melting slightly and during a pitstop and trying to fit another wheel over the top, while the wheel torqued up alright it did not last a lap and the wheel came off destroying , disc, caliper, wing etc. i would never run plastic spigot rings on a serious track car which is likely to need fast wheel changes, we had a ton made in metal and a tight fit into the wheel loose fit on the hub so we can centralise the wheel during a stop but they dont get stuck.
they are not load bearing, if they were they wouldnt be made of plastic, they are there to make mounting easier and centralise the wheel during that process only. they do not keep the wheel central once all the bolts are done up, the spigot ring at that point does nothing, the load is of course spread through the faces that mate, so the rear of the wheel and front of the hub, the wheel bolts torqued correctly spread the load evenly throughout the two faces so act a bit like one huge bolt.
i will always fit them if i can as it makes life easier, but would never worry if i dont have them available
