If you have even a glimmer of their future purpose, I'd put some on-theme content there. If they are exact keyword domains of some kind and you're generating significant ad income while they're parked, that would be the only situation where I might do otherwise.
If you have even one piece of great content you put there, I'd say start aging the home page and potentially attracting backlinks.
The gov't in my home country released a new 'thing' earlier this year. All it is right now is a three page outline, but I expect it to be fleshed out into a full fledged consumer niche product/service in the next year. I bought the name in a domain. Reminds me I better put up at least the gov't document for now.
Sorry to derail the thread, but I just typed in the name of the service in Google, and got a very interesting suggestion in the drop down. Interesting because it's not thename of the product/service but it's close - and I think it's actually what consumers would look for. And guess what - those domains weren't taken :). They are now.