Thanks for the feedback!
I'll figure out some resource requirements for the upgrades. I've noticed that the Undead make for a decent defensive force unless some Armored Swordman come along, then they just make level fodder and once the Swordmen start to level up they can be difficult to defeat.
I wanted the Dragon to be special which is the reason the energy requirement is so high. I haven't pitted it against the Tech Ballista Tower so I don't know if the Dragon is over powered or not.
Not only did I give Tech 3 castles, I also increased their starting resources. I did this because I always play Magic and I needed Tech to produce some units I could test on. I forgot to de-tune Tech hehe.
alex, I have some ideas for additional Tech units. Hopefully I can incorporate them soon.