Interesting, I've been doing just that for the last couple of years.
It's been a mix of partial successes and total failures, mostly failures. I didn't want to go the 'mfa' route for obvious reasons, so I try to make these sites in to something that actually is useful, and that have a sense of community about them.
Here is a breakdown of what you can make this way in a month based on adsense alone after several years of work, not something to be proud of, that's for sure.
It is very hard to make stuff that does not need maintenance.
pfn 3,203 18 0.56% €0.08 €0.26
leftsidebar 68 1 1.47% €0.00 €0.00
linkbar 72 0 0.00% €0.00 €0.00
ccm 1,012 2 0.20% €0.06 €0.06
dzleft 52,480 34 0.06% €0.03 €1.81
dzlink 47,804 98 0.21% €0.04 €1.87
dzmain 46,950 222 0.47% €0.17 €7.93
fls 90,839 459 0.51% €0.50 €44.98
gms 4,242 61 1.44% €0.31 €1.31
hst160x600 30,360 54 0.18% €0.20 €6.13
hst468x60 29,992 55 0.18% €0.20 €6.00
jks 359 10 2.79% €2.06 €0.74
lrmsmall 90 0 0.00% €0.00 €0.00
lrmtall 2,173,823 2,039 0.09% €0.05 €112.76
lrm 5,209 17 0.33% €0.35 €1.81
lrmlink 2,204,212 2,234 0.10% €0.05 €115.06
lrmlinkbar 24,719 109 0.44% €0.15 €3.64
mdcl 84 1 1.19% €0.05 €0.00
pcs 93,418 225 0.24% €0.21 €19.21
pcslinkbar 89,701 1,206 1.34% €0.43 €38.88
stroompunt 1,039 17 1.64% €3.60 €3.74
cams 1,510,897 5,889 0.39% €0.19 €289.18
ztk 27,112 711 2.62% €3.69 €100.15
ztklinkbar 28,534 462 1.62% €1.30 €37.10
These figures are for the month of January.
I've removed the ones that I consider total failures from this list or it would have been three times as long.
$1 per day per site sounds like a great plan in theory, but in practice it is quite hard to do that across a broad number of sites and not get bogged down in maintenance issues.
Anything with a form will attract spammers more than it will attract users, software will over time stop working because external things it depends on will change and so on.
Passive income is nice, but it is hard to make something that is really passive.
It's not a complete failure, but it definitely wasn't the success I expected either.
This is due to a whole pile of factors, maintenance has already been mentioned, lousy ECPM is another, inability to get any traction with some projects is a third (anybody interested in a complete platform for trading second hand cars or houses ?).