Virtual goods (i.e. in-game currency in online games) require something to be used for.
Just in real life, Money on it's own is worthless, it's just paper. Money is worth something when it is given away in Exchange for something else.
On SO, there is not much to exchange points for. Bounties is pretty much the only thing you can "buy" for points. The other thing you can "buy" are Downvotes, but that's hardly an incentive.
There are some notable exceptions though: Telerik is (was?) giving away their $1200 .net Package to users with 10.000 Reputation, which gives each point about 0.12 US$ value. Also, Jeff Atwood was (still is?) sending free stickers to users on the first two pages. And I think that users got a discounted price for SO careers, but I don't know if that was if you had X points of if you are just a user long enough.
But these are exceptions, not a regular way to "spend" the points.
Points would start being really worth something when
- There are more regular Giveaways of stuff to high rep users
- There is a merchandise shop where you can buy real stuff for points
- Companies use Reputation as a way to filter job candidates
I don't see that happening anytime soon, but I do see every now and then something happen where points are beneficial. So I wouldn't say that they are completely worthless, but also probably not that valuable either.