Another thing to think about is that your current Z is worth more now than it ever will be. Each day and each mile driven it drops in value. Maybe you can work out a deal that if you sell it, rather than trade it in, your husband will let you buy the one you really want.
I too pamper my motor vehicles (Hummer, Z, sportbike, dirtbike, and atv). I just tell my wife, it's either this or a mistress, your choice.
She understands.
Nothing wrong with trading for what you want if it's worth it to you. So what if you lose some cash in the process. If it's what you want, go for it. People lose cash all the time with no real benefit (i.e. smoking, drinking, gambling, sporting events). Too me, those example are a complete waste of money, but to some they are very important. Different strokes. It's your money, spend it how you want.
Good luck, I hope you can work it out.
WGW