Garry,
In rereading my post I wanted to be sure I was clear on one point. The requirements we had to meet do not vary regionally, they very from county to county and town to town around here. There just isn't a good way to know until you check locally, sounds like you and the Miss'es are already doing that. Reading between the lines, I would guess your Ag2 zoning is similar to what ours is for 5 acre or better tracts when dividing a property. At that point you eliminate a large number of expensive mandates. In our case, dropping below 5 acres mandated paved roads to specific standards, fire protection, county water (because of availability) and many other things. Above 5 acres gravel roads and wells would have been fine in our zoning. Our budget has reached an estimated cost of $9,400 per lot for development. Though certainly not guaranteed the family is hoping for a 40% better return on the land, after the investment, than selling it undeveloped. I only mention prices as a base of comparison. It helps me to have a ballpark idea of what to expect before my jaw drops when prices are quoted.
Like any real-estate purchase you have to evaluate the location, local demand and current similar land prices against the cost of development. Then you make your best guess as to what the future holds, put down your money and hope for the best. Here we can not expect the lots to sell overnight so it must be viewed as a longer-term investment. The situation could well be different in your area. Personally, it looks to me like you are on to something and I would put forth the effort to investigate it as much as I could. At the very least you will have a better education when looking at the next one. For what it is worth, we found the local surveyor to be one of the better resources when we started the process.
MarkV