I will give to you the same answer that was given to me in my early days on the forum.
It depends on the situation.
Yes, if you draw a  

 or  

 , your hand will improve, and you can riichi then.
Yes, if you don't riichi now, you risk losing a win if a  

  is discarded.
In this case, it is EAST 1, and there is still lots of time to win the MATCH.
If a  

 is discarded, you can still riichi later and wait for another one to come out.
What would you do if you drew a  

  or  

 . No more pinfu, but waiting for two different tiles. Do you consider that an improvement?  Is riichi and a dora enough?
I don't think there is a general rule etched in stone on what to do.
In this case, I would probably wait for some improvement before I riichi. 
Other considerations:
Am I dealer now?  Is this a Hanchan? Everything matters.
(And I'm sure you know this, but calling riichi doesn't always guarantee a win, you can still toss that winning tile to someone else.)