We thought of doing this when our daughter was born two years ago and I did much research on it. If you can afford the initial storage fee and then the annual maintenance fees then why not but we found it to be cost prohibitive at the time. The American Acadamy of Pediatrics says:
Cord blood donation should be discouraged when cord blood stored in a bank is to be directed for later personal or family use, because most conditions that might be helped by cord blood stem cells already exist in the infant’s cord blood (ie, premalignant changes in stem cells). Physicians should be aware of the unsubstantiated claims of private cord blood banks made to future parents that promise to insure infants or family members against serious illnesses in the future by use of the stem cells contained in cord blood. Although not standard of care, directed cord blood banking should be encouraged when there is knowledge of a full sibling in the family with a medical condition (malignant or genetic) that could potentially benefit from cord blood transplantation.
I would do some research on the subject before making a decision and disucss it with your doctor/pediatrician. Good luck!