Here what I typically see is maybe 50% of them are recent CPUs (because growth radically accelerated when the Fed did QE driving the bond investors to emerging markets to seek yield, with credit growing > 20% annually here) but only dual-core. Often only 2MB of memory. They are cheap machines but later generation, because they need the latest AGPU to play Dota, etc.
2 GB of memory?
Dual core (Intel) i5 CPUs have only 3 MB of cache, so they will mine Cryptonight at less than half the speed of the higher end quad-core i7s with 8 MB (which are roughly comparable with mid-range GPUs). That is assumes they are turned on and that they aren't in use such that mining needs to suspend or background itself.
All that conspires to make one of these machines worth a lot less in a botnet compared to a dedicated miner. Obviously botnets can be large, but I don't know how large. With the equivalent of 100K miners already on the network, it takes several hundred thousand of these in a botnet, at least, to become problematic from a security point of view. Smaller botnets add to the security of the network, which is
my primary concern, not economics.
I disagree with the economic argument about botnets being important "because they get cheap coins" for two reasons:
1. Botnets are a finite resource and if mining with them is so profitable because they get cheap coins more botnets will join the network until the coins are no longer cheap (a combination of botnets getting scarce and the difficulty going up), and 2. given opportunities to trade the coins will end up with whoever values them the most anyway. That may well be some whale who buys them from the botnet owner, or the botnet owner might himself be a whale. The rich get richer, (almost) always. It is fair that we agree to disagree on this point.
I will say one thing about what I think about Monero generally. I think it is a bloody mess, with lousy code we essentially found half-finished in some dead guys attic (to speak in metaphors). But what it does, it does better than any other delivered coin (by a wide margin), and I believe that many of the most serious problems can be addressed in short order (some already have).
In fact I would guess that the reason you pay so much attention to Monero is that you agree it is by far the best implementation of decent privacy on a blockchain that exists today, and therefore the closest to something you seem to think is important. It may not be what you think it should be, and it may not ever get to what you think should be done, but it almost certainly is the closest today and may very well be the closest in the future as well.