It's more what Apple say is the limitation. Nobody can stop you using Logic on two machines simultaneously - but you'd be breaking the license agreement.
However, if both your mac's share the same network then I believe only one version of Logic will be able to run.
For most virtual instruments and plug-ins it's best to re-install them on the new machine. But, if they're small effect plug-ins then you'll probably only need to copy the component file from and to: