When starting out with Z-wave I also made the mistake of thinking everything had to be secure… I would do everything non-secure except door locks and garage doors… it just creates unnecessary traffic and will end up slowing down your network… I will link the post from one of the resident Z-wave gurus explaining this if I can find it again…
As far as someone hacking a non-secure z-wave device to then open a secure device… unless you are a super secret spy…(sorry if I blew your cover) no one is going to waste their time doing that and just break a window or kick a door in…
Edit:
I’ll add the more detailed explanation if I find it