Silverstone - remodelled Maggots/Becketts. Monza - Ascari chicane (the only chicane to improve the layout). Hungaroring - extended start/finish straight to allow more overtaking into a tighter t1. Montreal - last sector remodelling which brought us the wall of champions chicane.
I suppose Francorchamps was a special case; it had been abandoned as too dangerous in its original form. And too long at some 14km. So the cut across the valley was made into a technical section, with the help of Jacky Ickx. It changed the nature of the track completely, but many now consider it the best track in the world, so in this case it worked.
_________________ Use every man after his desert, and who should scape whipping? Use them after your own honour and dignity.
I think only few tracks recently build from scratch survived without at least one layout change. Layout change is essential part of track lifecycle. The original character of all classic track is long gone. Any future change won't kill it, because it's already gone.
_________________ Any old sap can pull teeth from a dead crocodile. It takes a man to pull teeth from a live one.
Laguna Seca was supposed to be retooled some years ago to bring it to the 21st Century and there was take about possibly extending it a tad but it seems they were not able to procure the additional land and funds to do so and it seems to have gone by the wayside. Either way the track itself is quite nice and challenging, though it's a bit deceiving in that it feels like a shorter track even though it's 2.3+ miles long. I think it needs to be modernized a bit more to have greater run-off areas and generally bring it up to todays's safety standards across the board.
_________________ Second place is the first loser!