Jeremy saved up and paid for most of his 'jaunts' abroad. I don't understand what was wrong with him travelling abroad and seeing other countries before he settled down. Many, many late teens/early 20s go abroad either to the third world to work on projects or to Australia and New Zealand so it wasn't that unusual, especially with his public school background and education.
Don't think he was really on a labourers wage. Farm labourers were very badly paid but Jeremy with his free house and car as well as his wages was very comfortable at 24. I cannot believe the risk of killing all those people and not getting caught was worth it just to get a half a million quid a few years earlier than if he waited for Granny Speakman to die..... doesn't ring true to me.
True he was getting well paid for the work he was doing but he was not satisfied with his wages and wanted more. He was very jealous that his sister didn't have to work and was provide a place in london. He was exactly thrilled that his mother offered to pay for Julie to stay elsewhere. Obviously part of that annoyance is she would no longer be in his bed but he also was not happy that Julie would have been provided a free place.
For someone like him who feels he was being slightled to kill everyone so he would not have to work anymore and can enjoy the money right away and would get the entire fortune instead of having to share it with his sister or her kids is something that indeed happens.
So the notion it is implausible is not correct. Worse there is some evidence that suggests he was concerned about wills being changed.
If it is a matter of whether it is more plausible he did it or more plausible the grand conspiracy alleged to have occurred then hands down much more believable he did it.
The only thing more incredible than the conspiracy claims themselves is the notion that this conspiracy could occur without any evidence left behind to prove it happened.
All the supposed evidence that demonstrated a conspiracy occurred has turned out to be lies and gross distortions.