I didn't realize this until I played against some of the top 10 players. Then I realised they were all playing aliens so I thought that was the strategy. On the next few games I focused on Aliens and I won let's say 4/6 games. The 2 I lost was because I didn't score enough pyramids, I won aliens but I had 10 pyramids or so and my opponent had 20+. So I lost even though I had more Aliens.
So my conclusion here is: yes, Aliens are very important but you need to find the balance between pyramids and Aliens. And remember, even if you are not winning in aliens, you are still able to "control" the number of aliens your opponent will get by turning the cards. So maybe you will lose Aliens but your opponent will only score 3 or so.
That's the way I see it.
P.S. I like the game very much but sometimes it just feels that you are being unlucky and there's nothing you can do about it. And it makes me mad hehe.