I don't think Ron or anyone from the team decided to make any "safe" choice with this game. I think that they made the choices that they thought were best for the game they wanted to make and for a new Monkey Island game.
The music is a very important aspect of Monkey Island (one could argue the most important), all the games had at least one of those composers working on it, seems like a pretty obvious choice to me.
The voices were already perfectly cast and I doubt they had someone else in mind to do them, so why would they need to change them? Doesn't seem to me like this is nostalgia pandering, but simply that they had (most) of the casting job already done.
The returning characters were a thing since Monkey Island 2 (there aren't many important characters in the first game, but most of them return in the sequel) even though they are few.
The UI we don't know anything about really, other than it works with a mouse OR with a controller, and that they worked really hard to make the controller option worthwhile. I think this really shows how really willing they are to modernise the way adventure games are played in a modern era.
This leaves the art style, which changes in every Monkey Island games (even between the first two). If there was a safe choice with the art, they couldn't take it while trying to make a modern game. Pixel art is out of the question because they don't want to get the "nostalgia game" label that Thimbleweed Park got, so it was a choice of choosing an art style that suited the game. They decided to go with 2D probably because it gives a cleaner look and ages the game less (look at how Curse aged better than Escape and even Tales visually) and getting the guy who made Ron's favourite fan art and worked as an art director in very good looking games was the best they could do. Also, Steve Purcell, Peter Chan, Bill Tiller and many others who worked on the art of the first 3 games were probably busy with their other jobs so...
P.S. Also I'm new here, been lurking around since page 1 of this thread 🙃