Steam – Buying Item from A Steam Account without the game

It doesn't cost nothing - it costs time and convenience to create different accounts and log in to them all separately when you want to change which account you are using.

I searched through the User Agreement. I think you're correct in that this is not specifically prohibited. Similarly, using multiple accounts to purchase multiple copies of the same game and multibox is not specifically prohibited (to my knowledge).

If you are the kind of person that would actually want to play different games at the same time, it does make sense. However, I cannot think of a legitimate reason to actually want to play multiple different Steam games at once. I have a hard enough time being good at any 1 game I'm playing.

Should you be doing this? In my opinion, no. I use the community-oriented features of Steam all the time and the Cons you list would affect me greatly. Having multiple accounts would be a tremendous inconvenience for me, and I don't care about any of the Pros you list.

Exceptions: There may be some games where it would make sense to have a separate account for just that game. I hear you do a lot of sitting around in games like Eve Online; perhaps you would want to play Bejeweled while you wait for something to happen?

Once you've consumed the CD key from a retail title by associating it with a Steam account, you can't use it again.

Furthermore, Steam will not allow you to merge accounts or move keys between accounts:

Steam accounts can not be merged together.

Per the Steam Subscriber Agreement, Steam game subscriptions / CD keys are nontransferable and cannot be reset / moved between Steam accounts.

The only exception that I've ever found is Company of Heroes, where I've been able to give away my account keys to other people, even those purchased on Steam. They limit you to 3 transfers, however.