From looking up more usage, as it isn't a word I often hear, it seems by nature to be neutral, but context can direct it to be more positive or negative.

If I heard someone say it in conversation, it would put a lot of emphasis on the tone of the conversation to take the meaning. I'd imagine it being used more sarcastically, as it sounds like a fancy word for someone with shallow knowledge of a subject.

"John won't shut up about that trendy new art exhibit."

"Oh yeah, he's a real dilettante all of a sudden!" 😒

John had never shown interest in art before, but now that he saw it and either liked it or pretended to like it to show off his "higher appreciation of culture" than his friends now he keeps talking about it even though he doesn't know anything about art.

I wouldn't say it's impossible to use in a positive manner, but being dismissive feels more likely. If someone used it that way I'd feel I was potentially missing out on a joke at first.