I think your W is starting to realize that divorce MUST bring changes in lifestyle. This might be her wake up call that she must curb her spending, downgrade certain things, budget and realize that part of ending a marriage is being 110% fiscally responsible for yourself.
I stand my by initial thought - if you are helping out w/half the bills then the new car issue is her problem. You said yourself you are driving around in a 10 year old car and you will need a new one soon. So, you worry about funding your vehicle and let her worry about her own vehicle.
If you are paying half the bills why is she so behind on the rent? That makes no sense.
She has no problem coming to you for errands, extra childcare or money. She has no problems telling you how sloppy your daughters look when they are with you but otherwise, as I said, you seem to be highly disposable to her when you are of no use to her. She had no problem giving you all the junky furniture and essentially telling you where to live and what apartment to choose. So, basically, if she is not controlling you or needing you for a favor, she doesnt seem to be open to much else. Tell her to look in to the Cash for Clunkers program - if she is driving a huge car its not fuel efficient and there is no reason for her not to choose an affordable and reliable vehicle. Or, let her drown in more debt. Either way its HER choice.
Jesus would want you to be a strong man for YOU and YOU first.