No but to pinch your favourite analogy - its is part of the "bigger picture" the police trying to accuse him of spending his inheritance before he had got it.
The jury got to decide the bigger picture. The jury herd how instea dof being worried about his family he lied to police about Sheila firing all wepons in the house and lied about calling police before calling Julie and was talking to police about how he was going to get a Porshe instead of expressing concern for his family and running up to the house to try to go in.
While the jury can certainly wonder whether he was expressing how he was planning to spend the money he was about to receive as a result of the murders the more damaging aspect is the lack of concern for his family and the lies he told.
As a defense lawyer I would be much more worried about that aspect and trying to find a way to explain away his lies to police and the overall lack of concern. Of course how do you do that? If he really received the call claimed he should have rushed over right away or dialed 999 instantly and should have been pressuring the police to go in or trying to go take a look for himself. He didn't even put in the effort to try to force police to restarin him and stop him from going in for his own protection. Perhaps he feared they would not stop him otherwise he didn't think to do that.
The defense ultimately dealt with some of these issues in an odd way. Jeremy on one hand still insisted he dialed police before Julie but claimed at first he was not worried and didn't that only after thinking about it for some time did he relaize the situation was urgent and that he had better call police. This is the explanation for why he didn't go there right away and the delay in calling police. He claimed Nevill phoned him at 3:10 and clearly he didn't phone police until 3:23 or so thus there was more than a 10 minute gap and looking in a phone book for numbers doesn't explain that away. So he came up with the was not worried at first routine.
He didn't really provide an explanation for his lies to police, calmly talking about cars and not trying to go inside through a window (like he admitted he could do) to check up on them.
I think he made matters worse with the crap about not being worried at first because the jury knew he called Julie first in spite of his lies to the contrary and that made the call to her make even less sense than it already did.
The Porsche statement was part of a much larger problem.
In any event, if the defense was worried about the jury thinking Jeremy was telling them how he planned to spend the money he was to inherit from the murders the defense could have had Jeremy stress he was talking about a kit car and to discuss the cost of such kit. I have not seen all of Jeremy's testimony but what I have seen didn't do such and I doubt such was done because the appeal court would have likely mentioned it. The defense failing to do so and leaving the impression that it was a real Porsche unrebutted is not a basis to appeal the verdict.