I recently excavated my site for new construction and I'm on exposed granite bedrock for the entire footprint.

I'd planned a full basement with 2 storeys above- all icf walls up to the top plate.

Having already spent time and money on excavation I'm reluctant spend more on backfilling, compacting and  testing. My budget is limited and I'd like not to shoot an inordinate bulk of it on the foundation, though I definitely don't want to be haunted by regret either!

The bedrock at it's highpoint just off-center of the footprint is barely below grade and it all drops off from that point in all directions. The deepest point is 56"below grade. My soil type is sandy-gravely-well draining.

Are there any advantages (other than the obvious "bedrock foundation") of having the rock as the floor of my crawlspace?

I'm wondering if would benefit similarly as a home built into a hillside utilizing the consistent temperature of the earth or if it would be a heat-sink drawing energy from my home.

My primary concern is having a well-insulated and easy to heat home.

I'm located in upstate ny = cold and long winters

One of the problems I've seen with ledge basements is that watercan travel through cracks in the ledge, (sometimes this is only at certain times of the year) so make certain you have good stone & pipe drains around the space - inside and outside which drain to daylight. The second is the heat sink problem that you mention - having a 50o rock as your basement will draw out heat as fast as you can replace it. Pinning your foundation to the ledge will insure it won't move, but then backfill with some type of gravel and washed stone and insulate above the ledge with R-20 foam - spay or sheets- to thermally isolate the basement. The third problem is radon - so put 4" perforated PVC pipe under the slab and vent it out through the roof.

Wouldn't heavily insulating my floor be the way to go rather then trying to isolate the bedrock? I'm wondering if the mass of the bedrock and its heatsink qualities would be somewhat advantageous in that it would maintain a stable year-round temperature equal to the  temperature 6' down. Or am I chasing the wrong assumptions?

The cabin I live in now is on piers and at one time was open underneath. Even though insulated with R44 and sealed the floor was very cold. Once I put a skirt of plywood and polyiso around it the change was dramatic - much warmer. The cabin is much easier to heat and the crawl space stays above freezing.

My house design is passive solar and I need to approach this foundation with the high efficiency in mind.

Is the basement useable for living space or mechanicals or will it only be cold storage? Even with insulation abovethe ledge, assuming that the foundation walls are insulated, the basement should stay well above freezing. The issue is whether the temp 6' down (50o or therabouts) is what temp you want the basement to stay. There is another related issue about condensation; moisture in a cool space has the potential to condense, so it has to be and stay dry. Insulation will help with that issue.

No question that an ambient temperature under the living space of 50o is better than 10o. Putting the skirt around the crawl space is an excellent example of the benefits of stopping or at least slowing down air infiltration vs just adding insualtion (the R44).

So addressing the moisture and condensation issue... would I be better off isolating the bedrock or insulating my 1st floor and relying on that and the icf walls to seal the space against moisture infiltration?

If there's no infiltration of warm air into the space I'd think that condensation would be much less likely to occur. 

By isolating the bedrock might I have as warm a floor as I would by insulating the first floor and relying on the temp of the bedrock to keep the underside of the house at a stable temperature?

Backfilling several inches with river-rock with perf-drain for drainage and radon contorl, with a 10mil vapor retarder, and R10-R20EPS crawlspace floor insulation with a 1-2" rat slab ((or a full structural slab) on top of the insulation making it a conditioned crawlspace is a FAR superior solution than insulating between the joists. Joist insulation leaves the joist edge exposed to the humidity of the crawlspace, which may otherwise need to be ventilated to keep the radon levels low enough in a granite-bedrock situation. (Granite is a notoriously high radon emitter.)

Most of uptate NY has subsoil temps under 50F- coupling the house to the bedrock's thermal mass is far less useful than when the bedrock temp is 60F- it's a net heat loss, only useful during the cooling season, and a just a heat load most of the year. But if you need to move air under the slab to purge the radon as is likely, there's effectively ZERO benefit. Setting it up ahead of time to be able to actively move air through your perf-drain & bed of river-rock is a good idea. (Sometimes wind pressures alone will be sufficient, other times a bit of help from a whirlybird or venturi type stack turbine does it.) If you're building in heat recovery ventilation, venting the crawlspace as well as the rest of the house will also take the edge off the radon & moisture issues in a condotioned crawl.