Maikai, as you said in quotes:
"What about the son of someone that felt slighted by JR...or was jealous of him? A lot of the elements seem to fit someone younger, that perhaps had certain advantages."
I still think that the heart drawn on the business magazine points to someone older and involved with business. However, there is a chance that a University friend of JAR was studying Commerce and could relate to the business magazine.
""Southern common sense" from the note sure sounds like sarcasm to me----perhaps someone that goes way back---but it sounded more like a slam against southerners."
You have a point there. I still think there is also a chance that it is a possible hint of the perp's past.
"By the time you get to the last paragraph, the killer's true voice seems to come out, with all the sarcasm, and calling John by his first name....the writer seems to get more worked up by the end."
This would suggest to me that it is someone who has met John before on business and refrerred to him as "John". Not a friend but someone who crossed pathes with John's business. I don't think a younger friend of John's son would address him other than at first, "Mr.Ramsay".
"Would a middle-age man (or woman) really have the wherewithal and courage to enter the house?"
Yes, once that he decided it was the only way to relieve his ongoing anger and pain towards John. The ultimate revenge, how to spoil one's Christmas, by killing their daughter.
Here is my step by step reasoning (guided by hints left by the perp):
1. I am not a cop and I don't have the file, but from what I have read, the autopsy points more to garroting first and then the horrendous hit to the head. Chances are very great that a first hit to the head would have caused alot of blood loss. There was very little blood loss internally and the scalp skin did not break. Chances are very great that this was premiditated garroting and not just an accident.
2. As many have stated before, it would be quite a feat for either or both of the Ramsays to choreograph the Ransom Note, the heart drawn around John Ramsay in the business magaazine, the heart drawn in JonBenet's hand, and the previous Charlevoix incidents. Chances are much greater that it was a well prepared and motivated intruder.
3. It just does not seem possible that either of these parents could garrot their daughter and therefore it was an intruder. Therefore, the parents were honest about the ransom note and business magazine and the heart drawn around John Ramsay.
4. "Dirty Harry" movie references in Ransom note is the first hint primer to kidnap/murder crime movies and directs one to look further.
5. The heart drawn over John Ramsay in the business magazine (as in the movie "Ricochet")suggests that this is for revenge on business.
6. The heart drawn in the hand of JonBenet is the clincher. It is the confirmation that the perp got his/her revenge.
7. The murder happened the same night that the movie "Nick of Time" aired locally. This is too much of a coincidence. In that movie, the culprits (a man and a women) pretended to be cops, kidnapped the six year old girl and threatened the father to do their bidding (kill the governor) or the girl dies. I noted on another line that the clock struck just past 1:18 at a turning point in the movie. It might be that the perp was watching this movie at about 7:00 that evening and after comparing his/her miserable life to that of the Ramsays (made so public that month), the perp decided to put his plan into action. The perp was getting his revenge on something that John Ramsay was supposed to do.