You might as well try. The laws are all over the place on this and who knows how the judge will react.
The valet company is considered a bailee of your property. The bailee is liable for any injuries to your property from failure to properly care for or use it. The standard of "proper care" depends upon the type of bailment.
Bailees often print disclaimers on the back of the claim check in an attempt to either modify the standard of care or eliminate it entirely. In some jurisdictions, courts have held these disclaimers invalid. Don't assume that if the valet company points to the claim check your only choice is to give up. Not so.
In the end, the question is what duty did the bailee have and did he meet the duty. The mere fact that your laptop is gone does not necessarily mean that the valet company was negligent, although the fact that there was no sign of forced entry is a fact in your favor.
Let us know what happens. And don't leave your next laptop in your car when you give someone else the keys.