Hi Rachel,
I was in a similar boat when I lived in a condo. I joined/started a landscape committee to tackle almost exactly the issues you listed. We started with cutting costs with garbage and irrigation, used a volunteer crew to paint a peeling eyesore of a fence, and were just starting to build that kind of goodwill, before tackling the trickier topics, when I moved away.
I started collecting photos of places that were mulching, and/or composting and amending the soil with the plant materials available. In Vancouver, B.C., at Stanley Park, there was a lovely perennial woodland planting that had been mulched with copious amounts of maple leaves. The leaves were all raked or blown off the lawn and walks and into the trimmed garden bed. I thought it looked awesome. At another fancier planting right in downtown Vancouver, bird-of-paradise and other gorgeous flowers and shrubs were growing in some very obviously compost-enriched soil. You could see bits of leaves, twigs, needles and other humus building things as part of the soil underneath these thriving plantings. I took pictures of both, but alas, never quite got to a point where we discussed it with the HOA people.
--ground cover - with lots of pine needles it sounds like it could be a bit woodland-esque there, yes?
oxalis / wood sorrel is a nice ground cover, looks great, and it can be edible, too!
--fire danger/mulch - pine needles are a great mulch; and by holding in moisture, I would think they would lessen the fire danger - perhaps there are some studies on this somewhere?
--erosion/run off/pests - simple swales filled with rocks,
pine needles, or other mulch are amazing at reducing pests in standing water - we witnessed this first hand with standing water that was attracting yellow jackets; after we built a swale to manage the puddling, the yellow jackets decreased by almost 100-fold
--people - check out the work of
Sightline Institute for research to convince people, they did some particularly awesome stuff with
clotheslines, which are typically banned in HOAs
If you've already had complaints about your balcony, perhaps use extra care to make it as beautiful and attractive as possible. For example, in a permaculture system, we see brown, dead plant parts as a valuable biomass, even seeds, but others often see it as untidy. If there is a way to compromise on this, and trim away or hide the brown dead parts (if any) so that others don't see them and your neighbors see something more mainstream attractive, you'll likely have an easier time convincing folks of your ideas.
Best of luck to you! (Unfortunately, you're going to need it!)