As you may have determined by now, the playa is dry this year, and has been for several years now. It will have a sheen immediately after a rainfall, but it dries within a few hours. I wouldn't advise going during the summer, or anytime it's hot enough that storms will contain lightning, unless you are photographing from inside a closed vehicle. Also, if you plan to drive on the playa, keep in mind that the slightest rain will leave you stranded without traction until the lakebed dries.
As a consolation prize, dry playa can produce some nice dust storms...