I think you are exactly right about the major purchases. I have done quite a lot of reading and most "authoritative" sources say that the research leading up to buying a diamond can be months.
I *think* I remember reading that the average buyer of an engagement diamond takes about 8 months to make up their mind.
I actually have quite a bit of original content on buying diamonds, but that doesn't mean it's *effective* content.
One of the problems .. my site has quite a lot of content for precious and semi-precious colored gems, but so far I haven't been able find a good indy merchant with a decent product line.
Then there is the traffic .. IMO, marginal at 200+ uniques a day.
On the other hand, my users click a *lot* of "gemstone" ads on my Adsense ads.
I don't have any idea what level of traffic I need in order to get good affiliate sales.