I'd think you could drop min tech time to 4 (this would make researching the optionals more appealing), while using a system similar to the Middle Ages scenario, where the first tech of each age is untradable and much more expensive to those researching outside their specialty. I.E. Life mages get Life Magic I at regular cost, but Death I would cost three times the regular price. After getting through this barrier, Death II could be regular price and tradable. Repeat at Death VI.