If you are going to veneer over the old veneer make sure you sand it down to remove all the old finish and that the veneering glue has raw wood to adhere to. Also I would suggest you take the opportunity to add any extra bracing necessary by glueing on the inside and securing with screws from the outside. Add a little glue to the screw as you screw them in to assure they don't back out. Countersink the screws a bit and fill the countersink with bondo and smooth. I used this method on a set of 825's about 20 yrs ago and the veneer is still looks as good as it did the day they were finished.