It is a better source for material than the SE LD. Basically it is the same content, but with better quality video.
Don't let the PAL thing throw you off, as it is an easy recompile back to 24fps to use as a DVD master.
It could be a good place to get some of the orginal frames back etc. that were lost in the DVD release. It's a shame its not the original OT, but it is less bastardised than the DVD release, and so some recovery is possible.
SO by combining the two, you could get something that was closer to the original trilogy than the DVD is, with better video quality than the laserdiscs.
As for using it to splice into the original laserdiscs, the effect is so jarring as to be unwatchable. I don't quite understand the reasoning behind doing it.
On one hand you could argue that you are putting the best available frames into the original trilogy. But what is the reason for doing that?
I agree (kind of) that it doesn't change the film *theoretically* (i.e. you have the same frame count, and the same things happen on the same frames) , but in reality you get something that is just plain weird, and is unwatchable as a film. So really you end up with something that is much further away from the experience of watching the OT, than just watching the laserdiscs, or a straight laserdisc transfer to DVD. You are much closer to the original just watching the laserdisc.
If the laserdisc and the DVD and the HDTV version were the only copies of the film in existence anywhere, then it would kinda make some sort of sense to do it from a historical viewpoint - but it's simply not the case, the film has been archived at the AFI and other places, and on VHS in many versions and on LD in many versions - so I don't really see the point of it.
And before we get too pedantic, we should all realise we are archiving the Laserdisc release of the film (which has been modified from the theatrical release) and not archiving the film itself.