If you liked the movie, try reading the book. You may not like it so much after that. I personally thought the movie was a very poor translation of the book.
The "bald guy" was neither inserted as a tribute to Sagan (or being symbolic of Sagan) nor an alien sent to Earth.
His character (Hadden) is from the book (not added as an afterthought to the movie). He was supposed to have been a whiz kid who came up with a superfast computer processor (been a VERY long time since I read the book, but I think it was supposed to be some kind of intelligent processor) and other electronics and computer industry inventions that made him a billionaire. He was able to give the main character the solution to decoding and reading the information in the signal simply because he was still a whiz kid and his mind worked that way.
Unfortunately, while Sagan penned the character as an eccentric genius, I always felt the film makers turned him into a bizzare caricature. Zemeckis is a terrific directory, but Goldenberg's script needed more editing than he gave it. Turning a mostly narrative book into a solid movie is a very tough job, but I thought Goldenberg's script (probably exacerbated by certain of the actors) was stilted and ponderous and a disappointment after the book.
Sagan died about six months before the movie was released. He and his wife consulted on the film and he was able to at least see parts of film prior to its final editing. Pity that it wasn't as good a translation of his book as it could have been.