Properties of a good paella pan
I believe the dimples are for two reasons. One, they possibly help to make the pan, which should be fairly thin, more rigid. Secondly, they are a reminder of the time when these pans were hammered by hand - so, in a way, they make a factory-made pan seem more authentic.

The pan should be fairly thin, yet rigid, and conduct heat well. You don't want localised hot spots, but a strong, even heat.

The pan should probably not be too non-stick - you want to encourage the formation of socarrat - the slightly crusty layer at the base of a good paella.

The "how to cook" series in the Guardian are excellent for researching various recipes and deciding on an evidence-based amalgam - have a look at http://www.guardian.co.uk/lifeandstyle/2011/aug/18/how-to-cook-perfect-paella.