ik this is prob obvious but I'm putting it out there anyway bc I randomly got reminded of it
INDEPENDENCE & SELF SUFFICIENCY
Andrew spent all the money from Tilda's death on that car BECAUSE he didn't need the car - he wasn't gonna go pay college fees or groceries or whatever bc he didn't need Tilda to survive - he didn't need her while she was alive and he didn't need her now, he could support himself. So of course he wasn't going to use the money from her to buy essential things - he bought that ridiculously expensive car solely because he did not need it and he wanted the money gone.
Nicky jokingly mentions that the car is the reason they're poor, but Andrew wouldn't want Tilda to be the reason they're stable - they can take care of themselves. That money was never going to be used for things they needed, so he blew it on the car