Josh,
As to you staement that the cost of E and C being the same, well I disagree:
E = clearance/traffic for IFR, any VFR info available, so clearance for say 100 movements per months ?.
C = clearance and separation for eveybody, so all of a sudden the +2,000 (guestimated figure) odd VFR movments plus the 100 IFR = 2,100 per month would require clearance and separation, a hugely larger number.
You highlight (as we have done numerous times before) the paradox of E.
When the VFR traffic levels are low, they can (and should be) "in the system" ie C/D so RPT pax get the safety they deserve.
When VFR traffic levels get so high that they cannot be accommodated "in the system" and more controllers are required (increase in expense for C airspace) and E is theoretically the only ICAO airspace type that would "work" as VFRs have disappeared from the system, this means that the risk of IFR midairs with unnotified VFRs is so high that the risk would be unacceptable and therefore C would be needed to protect IFR.
My point: E airspace is a furphy and has no practical or safe application as far as protecting IFR aircraft from midair collisions with VFR.