This is something I'm trying to decide for my campaign right now. Sometimes it's hard to really know what's going on... We sell fairly high ticket products that are technology performance oriented, and I seriously doubt many people go straight from finding us to buying from us in one visit. So it's very hard to track what's really happening.
If your product is highly technical and not likely a first-visit purchase, consider ways to collect contact information for follow-up contact. White paper downloads, perhaps?
You do need at least two campaigns.
For your main (highly targeted) keywords, the ad should be broad, enticing and problem-oriented. That way, your CTR will be higher, and since the keywords are well-targeted, you shouldn't have a problem converting the visitors.
For the secondary campaigns targeting tangential markets, make your ads specific and solution-oriented so that you limit the clicks from people who are not interested. Your CTR will suffer, but you have better chance of being able to sustain positive ROI.
In the case of "golden apples" (assuming you don't actually sell apples, or oranges for that matter), you might go with variationis on "hesperides", "hercules", etc.
If someone is searching for "garden of hesperides", there is a probability they would be interested in golden apples. But of course they might be not interested. That's why you need a solution-oriented ad.
and not likely a first-visit purchase, consider ways to collect contact information for follow-up contact. White paper downloads, perhaps?
This is a very good advice.
Get their names and email addresses in exchange for a download of some whitepaper and then set up an autoresponder to follow up over regular intervals sending them more valuable information about the topic while lightly pitching them to buy the thing. This alone can tripple your sales and make it profitable to advertise in other markets.
I've created more ads over the last few days and honed things down a bit more. I'm bouncing around a 7% CTR. The data seems to show that sticking to the actual product with more directly related keywords seems to be working best. Within that, the most basic broad keywords seem to provide the majority of CTR and the more specific keywords aren't doing a whole lot... Same goes for ads, which kind of surprises me. The more generic ads are getting a lot more response than the much more directly targeted ads do. Which seems to go against what a lot of people experience. I guess it could be argued that the more generic ads are attracting more 'curiosity' type clicks though, and maybe the more directed ads will actually have better conversion.