Re: les pauls from the 70s and 80s, how do they compared to modern designs?
A few models use non-wood fretboards. That's not necessarily a bad thing; it's just not traditional.
There is a BIG dividing line between early '80's and late '80's Les Pauls. The early ones get lumped with the '70's ones, as Norlin products. Those were some of the worst guitars ever turned out by Gibson...but they are still okay, if you find one that speaks to you. The problem is that they have become expensive, which is completely ridiculous, considering that their poor quality is what basically started the vintage craze in the first place.
OTOH, the later '80's ones were made by the current Gibson company, and are significantly better...though they do usually have weight relief. Again, not a bad thing, necessarily.
To me, the best quality affordable Les Pauls you can get will be later '80's to late '90's ones. They were made very well, as the company was basically trying to restore the reputation of the brand that had been ruined by Norlin. In those years, I think they were made as well as Gibson ever made them. But Gibson got too big for their britches, and started cutting a lot of corners around Y2K or so. They have steadily gone downhill since. The pre-Y2K (or thereabout) ones are much better guitars, and much better investments, than anything Gibson makes now. If I was shopping for a Les Paul, those are the years I'd be looking at, no contest.