Yes, I've noticed that various Civs value the techs differently. In fact, I think it might even be related to the ammount of money they have total, as the Secondary Civs that come in with 5000 will give me most of that if I sell them my techs 1 or 2 at a time.

The tech trading is actually one of my favorite parts of this game. It is so much easier to do than in Civilization. The trades with the computer are much more realistic in my oppinion, which is why I like it so much.

In my last game (normal, large, abundant across the board) I ended up grabbing a lot of good planets early and got off to a tech and industrial lead that put me in the driver's seat. My income lagged far behind and I was running massive deficits throughout. I was able to offset this by trading techs constantly because the AI civs were running large surpluses. Had they put their resources into researching and building themselves up they might have had a chance. As it was, I was selling them things that they mostly didn't use as they passively sat while I took them out one by one, continually fueling my war machine with their surpluses. I'm going to turn up the difficulty a bit, but I think even on Normal the AI has got to be more proactive about developing their own solutions rather than just funding the player's efforts to destroy them. Had they spent their money and cut me off I would have had to be much more creative/strategic in forging my galactic empire.

It's easy guys... what "generation of that tech" is it? Laser II or Laser V? How long in general did it take you to research it? A little-bit or a lotta-bit?

Things like these give you relative values to the techs. Here's a few that the AI really likes:

Trade, Advanced Trade, Alliances, Governmental Research, Research Related Research, Factory Improvements, Economical Improvements, Habitat Improvements.

Get it? Any tech there is, the AI wants, and so should you. It's not difficult to get a good trade, and I often request credits along with the AI's tech because mine are worth more and I know it.

You can always click on a tech to see what it does

I don't think it's really that easy to say "tech X is worth Y". Things to consider:

-Laser III is going to be worth much more to someone without any Laser tech than it is to someone with no Laser tech
-Laser III isn't going to be worth as much to someone who's way up the tech ladder in missiles and has no current need to change.
-Terraforming isn't worth much to a guy with one mostly empty planet, but someone with 5 fullish planets would value it more.
-How much do you show a tech as being worth? The total research to get it? Just the research for that item above it's predecessor? The amount that AI player would have to reseach to get from his level to yours?
-The AI's tech capacity has got to figure into it too. A research-heavy AI player with 20 research bases isn't going to get much from you that he can't get quickly himself, but someone with little research capacity might be willing to pay over the odds.
-Effects of diplomacy levels, current relationships, alignments, bonuses, etc. have an effect....

I don't think any figure for a tech other than "how much the other guy is willing to pay/sell for at this moment" would make sense, and then it'd differ for each person you talked to.

Yes, the lasers/shields example there is another reason why (if the trading AI is smart enough) you can't really say what a tech is worth, since in theory it can change depending on what else is or isn't on the table.

I think what might work, and might be enough for us is to give us a button to press that does to the effect of "given what we have suggested for trade with the AI, what is the money they want to pay/be paid in addition", with an option to put that amount of money/influence on the table too.

You know, whenever I click on a tech to find out what it's good for, it lists the ship improvements, but everything else is pretty much blank. Prerequisites and Follow-ups.. From the info click, I can't guess the value because I don't know where it is on the tech tree.

Value also depends on your current situation.
In my current game I have a 700% manufacturing bonus on my home planet.
I have run out of tiles to quickly build a galactic wonder that would permanently protect my trade ships through the whole game(privateer),meaning I could hammer other races trades to weaken them without fear of reprisal on my own freighters.But researching it would take 39 weeks of research,unless I unbalanced my spending practices.
So how much is that habitat improvement bonus worth that would only take me 7 weeks to build in order to free up the space and make sure I get that wonder?Quite a bit if trade is one of your overall strategies for winning the game.