Wes:
Is a MMO any less of a waste of time as any other entertainment medium? Is $15/month a bad investment if you'll be playing regularly and derive as much enjoyment out of it as, say, a $60 game?
In this time of premium content in the form of DLCs we may well be able to get our value from a MMO depending on how long you play. I'll compare a MMO to one of the most expansive single player experiences in gaming, Fallout 3. For example, to get Fallout 3 and all the DLCs will run you roughly $100 (Canadian). And yes, people do pay for it. In fact MANY people have paid for it and are actually lining up to pay for more to add another $20 to that within the next couple of months. But right now, that'd be damn near 7 months of a MMO. Half a year and some change.
Most people will beat Fallout 3 and all of its content, DLC and otherwise, in a good couple of months assuming that you aren't unemployed with no social life (IE Me, where it took my about 2 weeks). Now if you think of a MMO, that's still 4 additional months before your cost matches that of Fallout 3.
Would you enjoy more 2 months of Fallout, or 6 months of a MMO?
Financially speaking, the MMO is a far better investment in terms of Time:Money ratio.
Now if you ENJOY one type of game to another, that's a far better justification rather than finances. Because really, we are really financially unsound in our hobbies. Or at least I am. I just spent about $300 on my Imperial Guard army in Warhammer 40K. On top of the $500 I spent on Paintball.
But I'm not about to claim I get anything from my hobbies. I don't play paintball enjoy for genuine exercise, I don't care enough about art to say I'm getting anything from the torture of painting little Guardsmen, and I don't write enough to expand my skills any further than they already are.
On that note, I really need to go paintballing again....