In both Civ3 and Civ4, the ability to trade for techs was game breakingly powerful. A disciplined and experienced player could maintain a full cash economy focused entirely on military conquest while using threats, conquest, and tech brokering to stay at or near the top of the tech tree.
This was bad, and resulted in Firaxis changing what techs could be traded for (from 3 to 4, removing the ability to exchange techs for cash over time and resources), adding a restriction mechanism to the AI (infamously known as WFYABTA, or We Fear You Are Becoming Too Advanced) that refuses to trade techs after various civ specific triggers are met, and even adding an optional disabling of tech trading with the No Tech Brokering option.
But then Firaxis added the ability to steal techs via espionage, which made things even more trivial for a military focused civilization, as many of the standard military structures produced the very points needed to steal techs. So, dyurr.
Elemental should not include an ability to trade for technology in the base game -- although it should remain available for modders. If it is included, brokering -- trading technologies received from another player to a third party for profit -- most certainly should not. Technology theft should categorically not be included unless the costs of doing so are greater than the cost of simply researching that tech -- if it is an option, it should be a less good option used when standard means are unavailable or insufficiently rapid.
What should be included, however, is a catch up mechanism for a technologically backward civilization in the form of technology bleedback. Each time one civilization researches some advanced tech, it should reduce the cost of that tech for all following civilizations that it has contact with so as to reduce the likelihood of a research focused civilization breaking away from the rest of the pack to such a degree that other civilizations are incapable of catching up. In the Civ series, especially on larger earth style maps, isolated civilizations -- especially those under AI control -- tend to get behind early, and remain behind forever. A bleedback system helps keep things under control.
To recap, the effects of tech trading and brokering should be carefully scrutinized before they are included. Magical or espionage related tech transmission should, if included, be more expensive than other, less dastardly mechanisms of acquiring technologies. Finally, backwards civilizations should receive benefits to research to keep them in the game.
