How can i plan a day-trip to Edinburgh from london in train and really make it worth?

Last time i travelled to London by train it took around 8 hrs though that's going back a few years so it's probably worth making a weekend of it.

You could get a sleeper train & do the journey overnight, sleep on the train, sight see then sleep on the train home.

P.s Glasgow is better, much less snobbery ;-)