Frank,
Therefor is "dirt road" airspace like G over D more cost effective than E or C over D?
Fair question. The answer, of course, is "of course, depending on the traffic levels".
However, I think G over D is more trouble than it is worth, because no sooner than I have left FL180 I have to get another clearance to enter the D CTR. It would be unusual to have a very heavily-trafficked circuit requiring a tower with no traffic in the mid, link levels, hence nobody is suggesting G over D. If a D tower is required, then some sort of controlled airspace would also be necessary in the link airspace.
We contend that that should be either D or C, since the cost of providing D, C or E will be the same (or close enough to be insignificant). The cost to VFR certainly is the same (radio and transponder required), so there is no skin off anybody's nose (apart from Dick's, who believes in "Free in GE, don't talk to anyone") and everybody gets the benefit of separation (C) or VFR traffic (D).
Win win, I say.
