I do not think the highlighted modifiers are generally redundant. However, I offer some alternative phrasings, which may or may not better communicate the intended effect, but more importantly are likely to provide some sense of the tradeoffs in different phrasings.
A possible alternative to
Gorgeous conifers stretched up endlessly, like pillars connecting the earth with the sky.
Conifers stretched up endlessly, like magnificent pillars connecting the earth with the sky.
Moving the modifier into the simile seems to give greater emphasis on "endlessly", which may fit a more awesome than lovely sense. This placement also seems to stretch the flow of the sentence (matching the stretching of the trees). Replacing "gorgeous" with "magnificent" further moves the sense in the direction of awe and away from loveliness, which may not be desirable. Replacing "the earth with the sky" with "earth and heaven" might fit a more spiritual tone, but it seems that the character may be experiencing a more worldly peace.
Pierced by sunlight, their leaves emitted a dazzling green glow which contrasted greatly with the grayness of their trunks.
could be rephrased as something like
Warm sunlight pierced their leaves, the dazzling green a breathtaking contrast to their trunks' somber gray.
"Glow" seems to have a softer connotation, which seems less fitting with dazzling. Replacing the somewhat generic "greatly" with "breathtaking" seems to intensify the effect and segues somewhat into the respiratory aspect of the next sentence. Adding "warm" and "somber" slows the pace again and softens the tone ("warm" brings a welcoming feeling as well). If these are pine trees, using "needles" might allow an intensification of the sense of heart-piercing beauty (but would seem to require other changes).
One different phrasing of
The air was fresh; it purified my lungs with every exhalation.
Every breath of the fresh air purified my lungs.
Using a simpler (but less precise) word in place of "exhalation" seems to fit a calmer tone. Using a single clause might well be less appropriate as it tends to hasten the pace and reduces the emphasis on the environment; by using "The air was fresh", an emphasis is placed on the environment. This phrasing would be more appropriate if the focus was more on the effect on the character than on the marvelousness of the setting.
Somewhere nearby, I could hear the chirping of birds, the chorus of cicadas—sounds that sank gently into my head, calming all my anxieties, dissolving every thought.
could alternatively be written as
Happy birdsong and a chorus of cicadas echoed through the trees, their sounds sinking gently into my head, calming all my anxieties, dissolving every thought.
This alternative increases the passivity of the character. Removing "nearby" may slightly reduce the sense of attachment/closeness of the character to the place, but this loss may be small. "Happy" does not seem quite fitting, but there seemed to be a need for a few soft syllables to provide a softer pacing. Using three participles seems to soften the tone and emphasize the gradual effect and the passivity of the character. Replacing "I could hear" with "echoed through the trees" focuses on the setting and increases the passivity of the character.
It was definitely a marvelous place
could be replaced with
It truly was a marvelous place.
In this context "truly" seems like a better intensifier because it has a softer, less mentally intensive feel than "definitely" (i.e., seemingly more fitting to the calming sense of the scene). By moving it away from "marvelous" the pacing of the sentence seems better, allowing both "truly" and "marvelous" to have more time/emphasis.
As Ice-9's answer indicates, such choices depend on the sense one seeks to communicate. In this case, using more modifiers than normal is likely to be appropriate both because this is an extraordinary setting and because such will tend to slow the pace (which is appropriate for a peaceful setting).
Putting the alternative phrasings together with the unaltered sentences gives a better feel for the strengths and weaknesses.
As I made my way uphill, I understood why An-Mei chose this place for her spiritual healing. I glanced around. Conifers stretched up endlessly, like magnificent pillars connecting the earth with the sky. Warm sunlight pierced their leaves, the dazzling green a breathtaking contrast to their trunks' somber gray. Every breath of the fresh air purified my lungs. Happy birdsong and a chorus of cicadas echoed through the trees, their sounds sinking gently into my head, calming all my anxieties, dissolving every thought.
Alishan had an uplifting, almost repairing effect on the mind. It truly was a marvelous place.
The paragraph break separates the more passive portion of the text and may increase the emphasis of the last sentence without the seeming awkwardness of that sentence being a paragraph by itself.