Hey Radi,
What you are talking about is hyperlocal content, which, if developed deftly, can be great for both visibility and conversions. However, if it's obviously a stretch to create this kind of content for a specific business model, it can end up looking really spammy.
Issa is on the ball stating that the content for these hyperlocal landing pages would need to be strong and unique, and this is pretty much where the rubber hits the road: does you client have something unique to say about his product/service in each of these hyperlocal markets, or is it really just all the same from one neighborhood to another?
You mention that your client sells plastic plants. My guess is that he is selling the same goods to each suburb, so unless there is something unique you can think to for each suburban audience, my concern would be that these pages might be being created for no other purpose that SEO. Sadly, as you've pointed out, a competitor is getting away with it. This is where Google lets SEOs down: teaching the business community that low quality is rewarded.
Can you think of something better for this client to do, that isn't low quality? Maybe video marketing? A social campaign? Acquisition of awesome reviews/testimonials? Something about businesses in each suburb that used plastic plants? What I'm urging here is to use your marketing smarts to see if there is a higher path you can take the client along, rather than agreeing that he should imitate a low quality competitor.
One thing to bear in mind with this ... that spammy competitor may be getting away with this today, but they've got a sword dangling over their head. They may be only one Google tweak away from anonymity. Should that happen, and should your client have invested his marketing budget in more interesting, creative work, he could find himself standing tall as others fall away.