The Catalan

What do you mean? 1.d4 Nf6 2.c4 d5? is bad, and gives white a clear advantage.

My point is just that you can't 'go wrong badly' in the Catalan, unlike the Ruy Lopez for instance. In one game I reached a roughly level rook endgame against an opponent 600 points higher rated in a classical game. No way would this have happened in the Ruy Lopez, or the Sicilian which you recommend for club players.

To play the catalan well need to be able to exploit very subtle advantages in some lines, for example arguably the most main-line one with be7, 0.0, and d5xc4. Here black neutralises the bg2 bishop simply with a6, b5, bb7, or bd7-c6.  Then plays the c5 break. White ends up trying to exploit the c6 square or some other small advantage. Other lines white has to be prepared for sharp play, with pawn sac. 

What white does have going for them is at lower levels the closed variation where black avoids d5xc4, and plays c6 is very popular for some reason. In fact the lower rated black players seem completely unaware of a whole range of the better black defenses, 

Also think lower rated players butcher the Ruy lopez, and playing something more straightforward like the scotch  would be more appropriate.