Well, considering you may not live long enough to see your kids into adulthood is a very real possibility starting out this late in life. Your life is about half over at 40. Even with the advances in medicine life expectancy really hasn't improved. 40 is still 40 even if the media tries its hardest to tell you its the new 30.
Another thing is while you may have more financial security you probably will have more work responsibilities also.
You also will not be in great shape. Most American woman at 40 or not in good shape. Some are, but they are not the norm, So you will not be playing with your child the way you could and should.
Also you will probably not see any of your grandchildren. Especially if your children follow in your footsteps. This is a major factor considering most grands help their children out financially, but more importantly physically with babysitting.
When a person wants to start a family it is up to them, but I think many people aren't being as realistic as they should be. There is too much uncertainty in life especially once a person hits the big 50. If a woman only starts having children in her 40's then she really risks leaving her children with an uncertain future should something happen to her. Even more so if mom is a single with no partner.
It is a cost analysis measure for me. However, if a woman is over 40 and wants to still have children and never had the opportunity before I would say she should go for it. My problem is when it becomes a fashion trend because it actually is not a good model. Their is a reason why the body is optimized for younger child bearing .... it is safer for everyone. .