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.
'after second thought'. In this usage, the colloquial form やっぱり can be used.
I am tired, but after second thought, I decided to go.
When I went to a bargain sale, it was crowded as I expected.
'as expected from the severe level of ...'
I am tired, but I am going to go as expected (because I have been absent for so many times, and it is severe now).
When I went to a bargain sale, it was crowded as expected (from the unbeatable deal they are offering).
'... (= a positive thing) expected from the characteristics'
It is tremendous of him to go even when he is tired.
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.