Does seeking worldly gains through worship or abandoning forbidden acts diminish one's reward in the afterlife, or is the reward commensurate with the intention?

A servant is rewarded for his intention. He must intend, at the beginning of every good deed, to please Allah and attain His reward. This is the sincerity (ikhlas) upon which the acceptance of deeds is based. Whoever performs an act of obedience or abandons a sin out of compliance with Allah's command and avoidance of His prohibition will be rewarded and recompensed. It does not harm him to notice a worldly benefit, as long as he does not intend ostentation (riya'). As for someone who intends only worldly benefit, without perceiving the action as an act of obedience or the abandonment of a sin, he will not be rewarded merely for the abandonment.