Choosing Between Different Tech Tree Designs

I am working on a semi-cooperative space game that has a technology tree module.

The tech cards have a resource cost and a general technology type (physics, engineering and society). They are "purchased" by using a research action from a common area with multiple face-up technology cards. Players do not have their own set of independent technology cards to research.

Obviously, more powerful technology cards cost more than weaker ones.

I have been experimenting with different designs using technology cards with these properties. Here are my experiments so far and the pros and cons I see associated with each one.

1) All the cards have a different back based on the type (physics, engineering and society) and are shuffled together into face down stacks. Two cards from each stack are drawn and placed face up during setup. When a card is researched, it is replaced with a card from the appropriate stack it originated from.

Pros: There will always be an equal number of cards for each type. In some instances, the card draws may provide players a choice of more expensive, stronger techs verse weaker, less costly ones. Cons: More expensive techs could show up at the beginning of game, be unpurchasable and lead to such cards clogging up a tech slot or cheaper techs showing up later in the game which by that point would be useless (and again clogging up a tech slot).

2) All the cards have the same back but are associated with three different levels (level 1 more basic to level 3 more advanced). First, all the cards would be shuffled face down into different stacks by level. Next, X amount of cards would be drawn from the level 3 deck, Y amount of cards drawn from the level 2 deck and Z amount of cards drawn from the level 1 deck and stacked face down on top of each other to form a new deck with level 3 cards on the bottom, level 2 cards in the middle and level 1 cards on the top. Five cards would be drawn from this new deck and placed face up next to each other. When a tech card is researched, it is replaced by a new card from this newly created deck.

Pros: more basic cards will show up first, and as long as techs keep getting researched, more advanced techs will show up later in the game (sense of technological progress albeit baked into the deck construction). Cons: Deck is reliant on all players researching techs in order to cycle through the deck to the more advanced technologies. Also there are no interesting decisions in regards to trying to save up for a costly powerful tech versus a weaker less costly one as the more costly techs only show up much later (choice is constrained).

After reviewing some space 4x board games out there, I noticed some of them introduced a rule whereby the resource cost for a tech is reduced by for the purchasing player by every tech of the same type that player already owns. This makes the more advanced techs prohibitively expensive thus forcing players to research cheaper techs of the same type in order to earn enough discounts to purchase it. At the same time, it still allows for players to save up, instead of getting discounts, for that one "big" expensive tech. This therefore allows players to feel that they are technically progressing while still being fairly unconstrained in the choice of strategy for gaining technologies.

I feel that Eclipse did a good job with their tech tree, but I did not like having to add X amount of techs a round which could result in tons of techs lying around. As such, this is my third idea I came up with:

3) I would introduce higher costs for the more advanced techs and provide discounts for players who owned techs of the same type. I would still have the level 1 to 3 technology decks and at setup draw three cards from the level 1 deck, 2 cards from the level 2 deck and 2 cards from the level 3 deck placing them all face up next to each other. When a tech is researched, it is replaced by a card from the same level deck (level 1 card from level 1 deck and so on).

Pros: Players still have the ability to go for the more costly techs versus weaker cheaper ones while still experiencing a sense of tech progression. Another pro is that only 7 tech cards are ever displayed. Cons: Not as much surprises for techs showing up (level 3 techs will not change for a long time).

This last option I have not play tested yet.

Of these three alternative designs, which ones do you like the best?

Are there any new designs you can think of that is better?

Any thoughts would be appreciated.

Thanks,

--DarkDream