PPC Overkill – Self-Competition?

Greetings,
My company is working with a major lead generation company which has provided us with a 17 page website. This is much more substantial than the simple landing page provided by most such companies. While they incorporate some organic SEO, most of the traffic, especially at the early stages, is PPC driven. We are spending $4K/mo., which goes directly to paid clicks.
We are thinking of undertaking another PPC campaign and while this would be targeted to a different (our main company) website, I’m wondering if doing more PPC with overlapping key terms, would be self-defeating, by boosting our CPC for all our campaigns. If it’s of any consequence, we are a plumbing and HVAC service company, servicing the Los Angeles residential market.
Thanks in advance for your input!

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