Don't have any direct experience with YC in a hardware context (only second hand), but in my experience the key to most hardware companies is the software (iPhones are great because of the App Store; Dropcam great because of their motion algorithms, etc). If I were to do the hardware startup I was involved in over again, I would have pushed for a greater focus on the software earlier on.

I could definitely see value in having equipment on site if there are still specialized tools you need for prototyping, otherwise if you're at a decently advanced prototype stage there are plenty of contract manufacturers within reach. Any top accelerator will be one or two degrees of separation away from them.

If you come from a primarily software background and are largely outsourcing the hardware side, I can see a hardware-focused accelerator being of particular value.

Just my $0.02.