LCG: Restricting card play through cost, actions or other methods

All LCG has a restriction system that prevents players from playing any cards all the time. For example,

- Magic the gathering has a cost on each cards and the sum of the cost cannot exceed your current mana.

- Netrunner has actions and a cost. So players can play a limited nb of cards according to the nb of actions they have and the number of money they have available.

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Now I have an issue in my game (that you probably have seen other post in the recent months). Both cards has a creature and a spell which each have a casting cost. The problem is that players will always try to find the optimal cost combination to play cards. For example, if you have 8 mana, you can cast spells with cost 4+4, 3+5, 3+3+2, etc.

But when each card has 2 casting cost, it starts to become overwelming to know what is the optimal pattern to use. I do like the double functions of cards even if it increase the possible permuation because It increase the possible strategy you can do with your cards. But it I could at least simplify the cost system, at least that would be one thing less to analyze.

An idea is to give each player a limited number of actions. For example, you can play 2 cards per turn. And the cost must be <= than your mana in play, but the mana is not depleted. Only compared. So if you have 7 mana, you can play 2 cards which have a cost of <=7. So the cost only "Unlocks" cards to be used rather than spending resources.

Another idea is to eliminate cost completely and make all creatures and spells even. I am not really sure about this one.

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I made a playtest with the rules above where players could play up to 2 creatures and/or spells <= cost and there were some interesting features.

- During a late game, low cost creatures are more likely to be used as spells than creature. SInce you cannot flood the board with small creatures anymore.
- If gives more control on the flow of cards in the game since you know how much cards goes in and goes out of the hand each turn.
- A huge amount of mana will not allow a player to empty his hand. Again more control on the card flow.

It could possibility create the following problems depending on the game.

- Run Away leader: If a player has more cards in play than his opponent, it will be harder to catch up since your opponent will always be ahead.
- Inpossibility to flood with smaller creatures giving less advantage to the player with stronger cards.

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Do you profer a cost based or an action bases system?

Is there other alternatives to cost based system?