Well I have something to say.... heheh......
the question seems to divide people on whether you want to know what your getting (to form your strategy) or the more realistic approach, that while you may have a general idea of what is around the corner, you still cant see all the possiblilties or applications.
So how about something in the middle...
What if on your tech tree you could only see say 10 years into the future, any tech that would require more than ten years you could not see and strategize for, but if it only took 5 years you would see it and be able to start building towards those tanks. You would see your tech tree unfolding before your eyes.
And it should not be just the tech tree. That is too specific, but an evolution in technology, thought and philosphy, social value, government, art, etc. Each a branch in a very dynamic matrix. You can then, using sliders, and bonuses for natural tendencies, decide where the percentages went in the above. But what you actually discovered would be a cumulative chance per round in each section. For instance you have 5% in this one and 20% in this one. Your spending much more on number two so the next round it was 40% likely to 8% likely. It would actually still be possible that you discovered both that round but neither is very likely. This very simple simulates the possiblilty of luck, breathroughs, an einstein appearing and so forth. And if you discovered like three techs in one round a golden age for a scientific civ.
But to really keep it blind in replayability, you would not always have the same tech tree. If there were many more steps on the tech tree, things were more gradual (say you discovered flight, then avionics, turbo prop, jet engine, etc or not just the spearman but the military strategy, after all many ancient civs came to power not simply by the unit but in the revolutionary way they were used) the tech tree could be huge, leaving you wondering how the tech world would look this game. So maybe some paths never opened up, you never found jet power, could not buy it and your spy got caught and executed for trying to steal it, so that that path just stopped. It adds importance to stealing because it may be impossible for you to discover it. Maybe you do not have a resource so you can study it (uranium anyone, so you discover they someone has it, steal it, and the discover the tech. This has happened numerous times in history and has caused the donwward spiral of many civs as a new civ with better ideas came forward.)
And as for unit upgrade and so forth due to the increase in techs, just make many automatic. Your tanks go form 6.3 to 7.3 to 8.4., etc automatically as you refine the technologies that would effect tanks: armor, more powerful arms etc. Only major jumps, would require an upgrade fee. (Although I hate upgrade fees, special sense you cann't just upgrade every unit at once like in SMAC.) The rest would be covered in normal maintence costs. Your paying alot to keep those soldiers with an nice new spear in 1500AD. Please. It would cost nothing to give him a gun (yeah maybe training, but considering that same spearman has been alive for 2000 years, I think I more than covered his training costs.)