In one case it would be easily replaceable by an -ing form, e.g. towers ashimmer => shimmering towers, weeds asway => swaying weeds. However, in some other cases, say, "its lush curves acquire new sinuous shapes as I lie asway, rubbing myself against...", a change to "swaying" seems a bit clumsy, especially if more present participles are heaped at one place - that might often lead to the semantic satiation effect and generally more monotonous sentences.
An extreme example to better illustrate it:
a) Using a-adjectives:
He darted out acry, scurrying under the velvety summer sky agleam, his scouring eyes atwinkle with emerging hope as the compound gate rose up aloom from the cringing silhouette of the sentient city asleep.
b) Using present participles:
Crying, he darted out, scurrying under the gleaming velvety summer sky, his scouring eyes twinkling with emerging hope as the looming compound gate rose up from the cringing silhouette of the sentient sleeping city.
I have conducted an additional Google search, I have found "ashimmer", but without the hyphen. Which one would be better, then?