Copying playlists and songs between iTunes libraries

My home computer infrastructure is currently in a state of transition, in which my recently-purchased MacBook Pro laptop is slowly taking over all of the tasks once handled by my aging (or ageing?) iMac desktop machine. 

I'm now finally confronting the inevitability of transitioning my iTunes onto the MacBook. This presents a particular headache since, for the time being at least, the iMac will remain the primary seat of home internet connectivity and is thus the natural place to, ahem, "acquire" new music. So what I need is a reasonably painless way to copy recently added tracks from the iMac iTunes library to the MacBook one, in order to keep the latter up to date with ongoing additions. I'd also like to be able to copy playlists (those painstakingly crafted distillations of listenable tracks tailored to specific moods and musical contexts).

Thanks partly to the fact that my iMac iTunes Library lives on an external hard-drive (due to lack of space on the main drive), it turns out that both tasks can be quite easily accomplished, using essentially the same procedure.

To copy songs:

1. In the "source" iTunes (the iMac) sort tracks by "Date Added" and create a new playlist containing all tracks added since the most recently-added track on the "destination" iTunes (the MacBook Pro).

2. Export this playlist (File > Library > Export Playlist...) --- I don't think the format matters, but I chose Unicode and that works.

3. Close the source iTunes, disconnect the external hard-drive from the source machine, and plug it into the destination machine.

4. In the destination iTunes, import the playlist from step 2 (you need to have copied it across or be remotely connected to the source machine). Now here's the cool thing: in the playlist, the location of the song file is given; since this is somewhere on the external drive, iTunes can find it and copy it across to its library.

To copy playlists containing songs already in both iTunes libraries:

Follow the same procedure, but this time, in step 4, iTunes is smart enough to see that it has copies of the songs already, so it simply recreates the playlist using these.

So all in all, not too much of a headache. I could try to be clever and write some AppleScripts to automate this process even further but that would be taking it too far...