There are some circumstances where one cannot be substituted for the other. For example, in the sentence "there are even more people here than I expected" you cannot substitute "all the more". In general "all the more" cannot be followed by "than". However, in the sentence, "If you don't want any pudding that means even more/all the more for us" or in a sentence like, "She is keen on horses, but he is even more so/all the more so" the two phrases can be used interchangeably.

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Hi, Raissa! I think there is not much of a difference between 'even more' and 'all the more', and they can be used interchangeably. Both of them are used to mean that something is even better than it used to before.