I also agree with xalt about making diverse technologies available via different methods. I don't think any should be random at game start however...
For the others... I see where you're coming from, but I still disagree. Yes, there are some survivors of the cataclysm. Most the champions you meet however, are not craftsmen. If you wanted to go the route of starting with everything and just needing resources for it, it takes away from the pacing of the game. It's more of an RTS feature, rather then a TBS one. Personally, I wouldn't feel like I had accomplished much of anything if I just needed to go kill those few things and wow nifty sword. Sure, you can still get nifty swords, but they're looted items, rather then one you just have waiting back at the city. One of the biggest joys in a TBS game is the diversity that tech trees allow. If everyone has the same exact playing field, the ability to make everything without research, I would find that boring. If I wanted that kind of game I'd go play Star Craft. (Star Craft is a good game, but I can't spend hours enjoying it like I did WoM or Civ)
Now, a compromise...your soverign starts out - say you're playing Ceresa. She's a mage. Do you think she knows how to work a forge? Doubt it. I could see the leader of Guilden knowing some about it though. I believe thats where racial starting traits came about. I think starting techs should be limited to what your leader would know about since in the beginning it's just the sov vs the world. This would include adding more to a character creation system so that custom leaders could have a certain tree available to them at start.
Over the course of the game, say you could meet NPCs/Champions who know other tech trees. In order to utilize them, they'd need to be hired on. Also, it would make more sense that if you were researching, that the champion that has that knowledge would have to be in a city and have proper facilities to do their research at. Also, you could find old blueprints from loots that unlock trees but still require a worker to do it. Alternately, you could have a hero/sov teach their basic knowledge to an expensive trainable unit called an Expert or something...who can stay in the city and do the research for you.
Now for the sake of not screwing people out of being able to start and get going, there should be base trees that every race starts with. The three available now are very broad ideas that cover a lot of topics. Going back to my Ceresa example, she may not know how to work a forge, but she would know the value of equipping her troops with good weapons. She would also know, being that she wishes to rule, about some basic techniques that would allow her to do so more efficiently. Being a mage, she would also (obviously) understand the importance and have some ideas on how to better use magic. Difference of knowledge vs common sense for the base 3 trees. I do think there should be sub-trees accessible under each one that are unlocked by items, or knowledge of certain npcs/champions that you hire on.
Basically - more specific example. The Warfare tree. It has to do with war. Okay? So what is war. War is a conflict. There really isn't much to war when just describing it as war. In terms of a tech tree, it should also not be as all-inclusive as it is. (btw, I like micro-management somewhat)
So...say you like spears. They're nifty. You stab people with them. Well, as a sub-tree of tech under Warfare should be something like Spear-Crafting. With more and deadly objects your artisans could learn to make, to hand to your soldiers to stick people with. Now you have a tree of spear items you can learn to make.
I hear the argument already. "Why learn to make? You have a blacksmith who provides the tree to do it! Why can't I just make my super person-sticker item NOW?!" Well, going back to the fiction. The Cataclysm. That blacksmith you hired on has probably been running for his life from random roving beasts and bandits and depraved survivors since then. He's probably a little bit rusty. So hire him, house him, build a nifty smithy for him and let him get back into practise by giving him metal and such to tinker with. Thus the tech-tree progression.
In the same breadth, you make can make very powerful types of units using your super-person sticker weapon when the blacksmith has gotten back into the swing of things. It makes the game more diverse. Instead of having 'Oak Spear', you could have "Mitrhil Spear' or "Legendary Ebony Spear of DOOM' on your side rather then just...'Oak Spear'. Which is the same thing your enemy has if they have just basic equipment. Also, each tech-tree advancement could be more player-sensitive. Say your super-person sticker item you want in the end does tons and tons of damage...but weighs a LOT. While the other guy could go a more middling, or a light approach for less damage but more mobility.
I'm just throwing ideas out here, fellas so don't take any of my commentary personally. I believe tech trees are an important part of playing Elemental. If they removed them, much of the draw of the game would be gone for me. I like the feeling of accomplishment when I can finally do things I could not before, or build things I didn't have the knowledge to do previously. It makes the game more fulfilling, rather then just a mind-numbing, 'race for materials then go slaughter the other guy' fest that RTS games are.