Revealing the Board

Using cards or hexes will make the number of habitable planets consistent but that might not be the problem. It sounds like the boredom may stem from the lack of decision making in this part of the game. If all planets have the same chance of being usable your only decision is to go to the closest one.

The solution would be to supply the players with motivations to explore certain planets. This could be open or closed information or a combination of both.

Here is a possible way of doing it and still use the dice. Each planet can effectively have two attributes; Color (Red, Yellow, Blue, Green) and size (Small, Med, & Large). Now have a deck of cards or chits you can draw from a bag with these 7 attributes.

During play there will always be 3 of these that were chosen at random. When a player attempts to survey a planet to determine if it’s suitable for a colony they can use any matching cards/chits to give themselves a +1 each on the die roll. If the roll is successful they are discarded and new ones drawn to replace them. This will give the players motivations on which planets to try based on the bonuses and by how likely it is that the bonuses will be available on their turn. If you want to give players more control you can have them replenish the bonus pool from a hand rather than randomly.

It seems that you could combine a number of these suggestions into one mechanic.

Like drktron, I tend to favor cards over dice because they offer opportunities for hand management and hidden information. However, for this particular game, I suspect that pre-placed tiles will probably do you the best.

As Dralius suggests, tiles allow you to have a consistent tile count. This is good both for game balance and component design since you know how many tiles to make. But it is also an nifty way to introduce an additional layer of strategy into the game. Once certain tiles have been turned over, the odds of finding any particular planet type changes. This dynamic often requires you to adjust your strategy in a way that no fixed random dice rolling can.

But, as OdysseyDyse says, the fundamental problem is not the mechanism but the payoff. When players take an action, they want a result. Provided that there are a number of different strategies that one can pursue, discovering the 'wrong' planet can be just as bad as discovering no planet. But, the difference between the two scenarios is that the 'wrong' planet is up to the player to decide. Perhaps it is just a 'different' planet than they wanted and they will change their strategy to take advantage of it. Or, even if it is useless, perhaps they can use their knowledge of it to their advantage (if it remains secret to other players). So... I would encourage every exploration even to turn up something.