We've just had one of the "our buyer wants your house" letters too, which I normally chuck in the bin.
However, this one peaked my interest and I called, mainly to get an idea of what a particular block could be worth. If it truly is of great interest, then the offer price should be good.
I'm waiting to hear what sort of money they are talking before getting too excited.
We were offered a fair price for each block, but two together allows development. This developer wasn't offering anything over and above what we would sell to a home owner who wants a big block to extend, add a pool etc.
We turned it down, and the next offer was $200K higher. (Does that mean we've made $200K in two days? ) That first offer was about $600K more than we had been offered about a year ago by another developer .
It still isn't really a premium over what we could get (according to the agent who took it to the developer). Added downside is that if we wait and get the DA through, we can spread the sale over three years if we ever want to sell. I prefer to sell the block with a DA and keep the front houses that provide us with income, or do the build ourselves. We have time to think about this.
It was a bit stressful though, not knowing what would come of contacting the agent. Ultimately, even if we had been offered another $200K again, we pretty much would be handing it back to the tax office.