I've left the plastic disks on the two Trek mtn bikes. Seems like a good idea given the single track and weeds they play in. I left the one on the CAAD3 R600 cuz I never got around to taking it off. That wacking great shinny disk is still on the Varsity but it sorta goes with that steampunk like RD, eh?
When assembling the rear on the Raleigh Pro Mk IV, I noticed his Majesty's frowning Lord High Executioner standing there with the razor sharp axe so, "I can take a hint", I left that one in the bin (the tip, not the parts bin). Looks great without it.
The Nishiki International had one of the shinny Suntour steel disks. First thing I noticed was that the thing sang like a National Steel guitar with every shift so it came off PDQ and is stashed away.
I don't hate em but they have that Gov't DOT/CPSC mandated look about them so I they don't belong on a great C&V road bike. They belong in the cellar with all the plastic reflectors.