I would advise putting a "that" there because "concluded" could be a transitive verb and "a hefty devaluation" could be mistaken for its object; when we realise it is not the object as we read on, we mark the writer down for not writing in a clearer manner.
The rule is that for certain verbs - such as know, hope, believe, feel, say - the "that" may be omitted. For other verbs, we judge the omission by whether it will mislead or confuse as we read quickly in a smooth forward flow. If we need to stop and go back as a result of the omission, then we conclude that the omission is a bad one.
See this guide from the BBC: http://www.bbc.co.uk/worldservice/learningenglish/grammar/learnit/learnitv336.shtml