More than buildings, which can revel in aesthetics or craft, public spaces need a shot of common sense to succeed long-term. If there isn’t some reason to be there, week in and week out, even well-designed spaces can become voids once the novelty fades.

Keep that in mind as City Hall begins to debate a makeover of Harvey Milk Plaza that is being sought by Castro district property owners and community advocates.

The aspirations are admirable for the small area that now serves as the entrance to Muni’s Castro Street Station. There’s a lot to like in the conceptual design that on Monday will be presented to the civic design review committee of the San Francisco Arts Commission. But the location is awkward, at best, in terms of a plaza intended to be a tourist destination and local gathering space, especially in a neighborhood with so many other draws.

The updated plaza would replace what now is a sloped landscape that runs from the corner of Market and Castro streets west to Collingwood Street, a residential lane that is 16 feet higher than the lively commercial strip below.

At present there’s a mini-plaza at Castro Street with steps that lead down to an open courtyard outside the station entrance and a ramp that leads west. The ramp passes above the garden on its way to Collingwood Street.

The station was under construction when Milk, San Francisco’s first openly gay elected official, was assassinated at City Hall in 1978, and it was dedicated in his honor in 1985. The now-iconic rainbow flag was installed along the Market Street edge in 1997.

However, the only historical details on Milk that a visitor will find are a bronze plaque at the entrance and captioned photographs on the garden’s wrought iron fence. The plaza itself, designed as part of the Muni station by Howard Grant, is a modest portal that has been stripped of such basics as benches.

The vision for the “new” plaza is much more ambitious: “equal parts memorial, celebration and call to action,” according to the presentation prepared for the Arts Commission by Perkins Eastman, the concept architect.

It emerged from a design competition held by Friends of Harvey Milk Plaza, an offshoot of the Castro/Upper Market Community Benefits District, which is funded by an assessment fee on property owners.

“We feel like it’s our responsibility to honor Harvey Milk, finally, in the plaza that bears its name,” said Andrea Aiello, the district’s executive director.

She also mentioned a more pragmatic objective: “This is a way to bring people to the Castro, and keep them in the Castro.”

A new plaza? For more information on the proposed makeover of Harvey Milk Plaza, go to www.harveymilkplaza.org The San Francisco Arts Commission’s Civic Design Review Committee will receive an informational presentation on the conceptual design for the plaza at 2 p.m. Monday at 401 Van Ness Ave., Suite 125. Full details are at www.sfartscommission.org

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Near Collingwood Street there would a triangular grove of 11 gingko trees, one for each month that Milk was in office. In the middle, the enclosure for a new elevator next to the rainbow flag would double as a canvas for graphic displays.

To the east, a gently angled amphitheater would ascend to a rounded edge facing Castro Street — an aerial perch where, it is hoped, visitors might seize the chance to “speak their minds, be heard and create change.”

In a more practical vein, the rounded perch would offer protection from the elements for the relocated escalator, stairs and courtyard below. The sidewalk along Market Street would be widened, and there’d be a separate path from Castro Street to the main plaza.

“There’s a lot that would be happening in the space,” admitted Erich Burckhart, who heads Perkins Eastman’s San Francisco office. “We want to tie it together into a singular composition.”

In the abstract, the firm did a good job. The design has a compact power as it layers distinct spaces in a way that allows visitors to choose their desired ambiance, be it solo contemplation or more communal settings.

But when you try to imagine the redone plaza in the actual context, the case isn’t nearly so compelling.

A big reason that Castro Street endures as a mecca for visitors and locals — gay and straight — is that you’re plunged into what feels like a boisterous village center, hemmed in by buildings and hills yet bustling with colorful life.

Contained and cosmopolitan at once.

The proposed plaza, however, would only succeed if it pulls visitors away from the action, west toward Twin Peaks — the topographical feature, not the tavern that is an official San Francisco landmark and was the city’s first gay bar not to hide itself behind blacked-out windows. Seated in the amphitheater, you wouldn’t see Twin Peaks Tavern or the Castro Theatre with its ebullient marquee, or shops and restaurants with come-hither names.

One piece of the proposed plaza is essential: the elevator from the plaza down to the subway platform. It would help to make the station more accessible, and the city has already has earmarked funding for it.

But if the desire is to celebrate Milk’s life and legacy, it might be easier to freshen up the current plaza and create an ongoing fund for its maintenance. Then, install plaques or informative artwork along the bridge-like walkway to Collingwood Street, a path that has serenity despite its surroundings.

This being San Francisco, no decision will be made anytime soon. There are sure to be multiple stops at the Arts Commission. Reviews by the Planning Commission and Public Works lie ahead as well.

“It makes sense for Harvey Milk Plaza to have some kind of memorial honoring him, and some sign that you’ve arrived in the Castro,” said Rafael Mandelman, the district’s supervisor. That said, “I still think we’re in the early days (of any redesign). ... Honestly, it might be dramatically changed by the time there’s an actual project.”

Mandelman is right — there’s a long way to go. And design for the sake of design is not the answer.

John King is The San Francisco Chronicle’s urban design critic. Email: jking@sfchronicle.com Twitter: @johnkingsfchron