(It's been a week, but hope this helps)
There are plenty. Consider:
In these phrases, the functions of
時常 are mostly apt to be seen as adverbs. This being said, the POS in Chinese is not very well-agreed.
This is due to lack of morphological markers.
In the ancient time there is no
地 marker, and adjectives also functions as adverbs (like German).
In these cases, arguably they also look like the complementary adjectives of the subject.
I guess its advent is probably 20 century, when phrases are so complicated that we often have difficulty parsing, and English-like structures are borrowed into written Chinese.
So back to the question, I would say that when a adverb doesn't cause ambiguity,
地 is often not added. The examples
In (b), it cause some confusion (at least when the eye has parsed to
兴奋 functions as. But in (b), suffices to say,
地 clears up confusion by reminding you a verb is following.
Last I shall note that even scholars often disagree, as modern Mandarin grammar is not well restricted, and native speakers are generally very tolerant with non-standard phrases.
I found a discussion. You shall notice that the general consensus does not deem
地 to be not compulsory.
地 from an adjective if the adjective is several-Charactered (so more difficult to parse), or when the phrase is complicated so that confusion arises.