In such a sentence as 「疲れているが、やっぱり行くつもりだ」, can you substitute やはり with さすが, with the meaning of "as one would expect", "also", "as I thought", "still"? How would the meaning change in this sentence? I can't grasp the real meaning of both adverbs in their daily usage.
'as expected from the severe level of ...'
'... (= a positive thing) expected from the characteristics'
I don't have the reputation to add a comment, so I'll post a reply.
I think it is best to think of やはり (typically) as essentially "after all...!" For example, your friend said he wasn't very hungry but he ended up eating a lot: Yahari, onaka suiteita!
On the other hand, さすが has a very nuanced difference. I like to think of it as something like "that's sure like [him/her]!" Again, this is a typical use. A situation where you often hear it is, in the same situation, your friend says he isn't hungry but he eats a lot: "Sasuga, Jon da ne!"
While these sentences look very similar, the nuance is slightly different. In the first instance the expectation was different from the reality, so we were left noticing something important after-all. In the latter case, we know that Jon is a big eater, and we expected him to eat tons despite the fact that he said he wasn't hungry. So Jon eating a lot confirmed how Jon-like his action was.
As you can see, both might be possible but the nuance would be different. やっぱり行くつもりだ。implies that in then end, you're still feeling like going anyway. / さすがに行くつもりだ。 would imply that you're just the type of person who goes even when tired.