It's free to invent anythings for readers but there is no mention about ghost in "Norwegian Wood". You can pick up negative images in the book. But I cannot find any negative signs from the following very end of the book.
"Again and again, I called out for Midori from the dead center of this place that was no place." by Jay Rubin
"I held onto the line to Midori from there in the middle of nowhere." by Alfred Birnbaum.
Important point is Toru continued to call Midori.
You can read the sentences between the conversations between Toru and Reiko.
"We are alive, she and I. And all we had to think about was continuing to live." by Jay Rubin
"The two of us were living and I had to believe we'd go on living." by Alfred Birnbaum.
I think it' very positive sign.
Nick, you wrote about sex 4 times of Jay's point of view. I may be very slow to realize "4 (shi) => death" but we read "4 times" as "yon-kai" not as "shi(death)-kai" in Japanese. I think Jay also was looking for some negative images there.
"Norwegian Wood" was published in September, 1987. Toru was 37 years old then. It means Toru is the same age with Haruki-san. Average wage in Japan was about 300,000 Yen and 1 US$ was more than 150 Yen. "Germany again." Toru travelled to Germany more than twice, arriving at Hamburg not Frankfurt. Trips to Europe were beyond our dream at that time. He must be very successful businessman, musician or something.