I agree we need content, but it's the domain owner who decides whether to develop or park. If you own the domain, it's your choice because you own it.
I have several names which I have no intention of developing, but intend on "holding and parking" until I'm ready to sell.
Nothing wrong with that, look at how many .com's are parked. If the big corps start promoting and using .mobi, good names will be worth a lot whether parked or not. Nothing wrong with speculation, just use your head and realize that there's not too much left out there to hand reg that would be worth anything EVEN IF .mobi became the next .com.
If you really want to get into speculation, I would advise buying names on the aftermarket, where good names can still be had for a few hundred bucks.
Better to spend $300 on one really good name on the aftermarket than to spend that same $300 hand regging 30 sub-par names, which by the way need to be renewed every year. Renewing one name is a heck of a lot cheaper than renewing 30, especially when that one name is better than the other 30 combined.