The concept of warming a car up, is primarily due to the carberators of yesteryear. A 'cold' car simply wouldn't run right until the air around the carb was of sufficient temp so the air/fuel mixture was right.
In today's fuel injection, the computer controls all of that, so it's much easier to run 'em cold.
Yes, there are some issues with wear and tear, but in my lowly opinion, you have more wear during startup due to lack of oil (until the oil pump starts) than due to heat expansion rates of dis-similar metals.
So simple common sense comes into play. Drive the car like you want it to last. Gentle is always better than abusive. Easy is always better than hard.
Now once they're up to operating temps, then have fun.
1992 YJ, 401 V8, EFI, TH400, Atlas, D60s, Detroits, Warn 8274, Cage, 37 Krawlers
1997 TJ, 350 V8, EFI, TH400, Atlas 4spd, D60s, Detroits, Warn 12000, Cage, 40 Kevlars
TTC 1994, TTC 2012, Trail Tour participant.