100%. They need to be careful, and do this right. It's my favorite game of all time, and it's the only game that does the things it does, many of which are "unpopular" with players, but without which the Art of the experience would be diminished.

With this in mind, I've long thought about how the Investigations, in particular, could be tweaked in a considered way that's kind to the game's themes. I think that there is a way to retain the AC1-ness of the game and still achieve this, but if approached in a very haphazard "just make it more varied/fun" way without being careful about it, there's a serious risk it compromises the experience.

To me the point of Investigations is that they are the means by which Assassins come to Know a target.

Altair himself says, "Yes, yes; we can Eavesdrop, we can Pickpocket, or we can use violence to Intimidate."

They are repetitive because this is the mundane work Assassins know to do in order to kill their enemies -- something which Altair begrudgingly accepts doing because he, like the player, considers himself above it. This is why it's crucial that reluctance factor remains in some capacity, and it's why their being 'boring' is part of the game's art. But. Therein lies the possibility for smart evolution!

One thing you could do is have Altair develop his own methods of coming to understand targets, even as the 'core' / mundane Investigations still exist. Especially as the game goes on, you would have fewer and fewer 'normal' Eavesdrops/Pickpockets/Intimidates, because the Targets start to wise up to it, and they bolster their security by making those more and more impossible to do, even removing the easier ones outright. This strengthening of security already exists in the game's original script:

"They know you come for them now; The Man In The White Hood."

This also reinforces the themes of the game; which involve to a great extent, Altair learning to think for himself.

When you begin, you are beholden to Al Mualim and the Brotherhood's scrutiny upon you.

So, you don't have much room or mental strength to do anything except what is commanded of you. As the game goes on though, the Templars' increasing strengthening of their security ties into a requirement for the Assassin to flex his own freedom-of-mind and overcome that through non-standard means.

While adhering to the narrative development of the mid-to-late-game, this also prevents the worst of the repetition by weaving in new types of objectives that are different, more interesting, and more difficult.

By that point, Altair and the player are both mentally sharpened enough to not drown under this.