It’s a free-for-all at a city park surrounded by homes boasting million-dollar views — with locals brazenly swiping plants and even gravel from the long-neglected green space to beautify their own properties. The illicit activity at Queens’ Powell’s Cove Park — which has included homeowners chopping down city trees to improve their vistas, as The Post previously reported — has only surged as warm weather creeps in, outraged residents said. Powell’s Cove Park has become the site of rampant thefts and vandalism, according to locals. James Messerschmidt In one of the more brazen daylight thefts, an elderly woman began “stealing the path” in the park lined with gravel — right in front of a local environmental group whose same volunteers had recently performed $13,000 in taxpayer-funded work to refurbish. “We were doing an assessment for a cleanup that we were planning, and we heard this noise.…