The re-use of found materials in garden spaces is an important idea. So many intriguing and useful containers, plant stands, stepping stones, retaining walls, furniture, trellises, and of course 'pure' art, can be made from society's discards.
Even cardboard mulch, shredded or whole, would be an example of such DIY re-use.
Rather than bemoaning the chips, scuffs, and rust of re-used material, we should recognize it as value added. To intentionally add such rustic patinas and effects on new materials requires added time, material and labour. Furthermore, the bespoke effects of time, individualize what was once mass-produced material, thereby turning the ubiquitous into the unique.
Whether any such creation would be considered 'steampunk', or any other style or genre, is a secondary aesthetic debate.