I must disagree somewhat. I do agree that prepwork is important but I'm sure Vendo did just that, so a re-paint over original will still have a good base to it.
Chips should be filled rather than sanded smooth though, to avoid a wavy finish but if the old paint hasn't peeled or cracked in 50 years, I usually don't remove it. I did take a multi-layered Pepsi machine in to be sandblasted 2 months ago and the guy warped the side of it trying to remove decals.
Two exceptions, and the first is rust removal where blasting is preferred but will surely take the paint off with it. Secondly, is blasting the embossed letters and surrounding areas as removing prior material will result in them looking much deeper and clearer. I just use a small home blast unit for this.