In short, not worth. PPC is not SEO. Google likely knows that installer and fitter are synonyms. The relevancy portion of your QS, which is about 25%, will likely not be affected.
As for making it work, there is a learning curve, although it seems that curve is getting steeper. That's why many fail. It's not as easy as the search engines would make you believe. Yes, it's easy to just write in some keywords (most use the wrong ones or are way too generic) and write a short ad (most are bland and uninspiring). But to put everything together and generate a profit, that's hard.