The poet takes this blue dye as a simile for a new fashion in literature, and points out that Hobbs, Nobbs, etc., obtain fame and comfort by merely using the dye from the shell; and adds the perfectly natural comment:-- "...

Who fished the murex up?
What porridge had John Keats ?" So that the verse is not subtle, and was not meant to be subtle, but is a perfectly casual piece of sentiment at the end of a light poem.
Browning is not obscure because he has such deep things to say, any more than he is grotesque because he has such new things to say.

He is both of these things primarily, because he likes to express himself in a particular manner.

The manner is as natural to him as a man's physical voice, and it is abrupt, sketchy, allusive, and full of gaps.
Here comes in the fundamental difference between Browning and such a writer as George Meredith, with whom the Philistine satirist would so often in the matter of complexity class him.

The works of George Meredith are, as it were, obscure even when we know what they mean.
They deal with nameless emotions, fugitive sensations, subconscious certainties and uncertainties, and it really requires a somewhat curious and unfamiliar mode of speech to indicate the presence of these.