Micro sites are a very profitable business model depending on what your goals are IE: earning via clicks ( cpm/cpa ) model or Lead generation model.
My earnings model was mostly lead generation, with product purchase as a secondary, and click revenue as third.
my exit model was to sell it to the manufacture or vendor of the niche I was in.
when I was ( still have a few ) in that game, I was able to consistently rank high for the niches, I would spend a great deal of time before I choose a niche of figuring out whom to sell it to.
one niche in which I was dominate with micro sites ( I don't have anything anymore sold it as a portfolio sale ) was ford auto parts for mustangs from 65 to 71, for some reason I was able to dominate it with ease and could get content consistently and get product buyers leads by the ton loads ( You really don't know how many types of hoods mustangs have ( plus the parts related to it ) until you really do the research, and you can get them in fiberglass also. had about 10 vendors just buying those leads at 1.50 each or direct purchases from my sites as affiliate accounts.
one thing that I can tell you is that you need to be amazingly careful with adsense. my rule back then prior to getting really big with a few site was:
a) never have more than 200 sites on a server
b) match all those sites to adsense
c) get permission from google analytic so that you can track all 200 web sites
d) everything under 1 LLP, going to 1 bank account, going to 1 phone number and 1 mail drop.
I never had any problems and I was real happy.
once I had reached a better traffic volume from google, they let me build more sites out to a specific name and never worried.
selling my sites was the easy part, you are making 7K a month, then sell it for 36 times earnings, start at 50 times ... here is the logic, if you are making 1.00 per lead, that lead is really costing them about 1.50 ( that's a 50% cost increase) then if our leads are converting reasonably well, they are making on that 1.50 about 17.00 to 50.00 ( in mustang market ) or maybe even more, but my research told me that I had to work on this factor. so I picked up the phone with all my numbers and the traffic, converting traffic and any notes. easy sale, and if you do it correctly, they will ask you to build out sites for them in niches that they pay you directly for all the leads ( got a few of those, my favorite was for very specific type of big block that could be shoehorned into a mustang, and the leads paid out 8.00 per each one )
Another great hit for me that made me serious money, was a product that paid out $25,000 ( yep, 25 grand USD ) when the lead converted to an investor, and every lead generated on my sales funnel ( seven pages ) was paid out at 5.00 . those guys were nuts, but they could take the lead and convert 4% from my leads while others converted at 1% or less. That company loved me. Sold my site to them for a fortune.
Oh that above mentioned site, is in the immigration niche, so now you don't have to PM me about it. ( I'm long gone out of that niche ), and it requires that you make phone calls to get into it.
as for the income that niches made (make) me, the low end about 10 a day, high end 1800 per day, the bell curve is left heavy with the peak at about 78 per day.
there is more to talk about but that's for another time.
Billy Good