This involves math.

Let A = expected production for the remainder of the reset from the new land gained
Let B = expected cost of grabbing said new land

If A exceeds B, then it is correct to grab.

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Let Q = amount of new land gained.

A is calculated by (Q) * (goods produced per acre) * (avg price of good you will sell it at) * (number of turns left in the reset)
A can be adjusted by other things like Market Commission, and/or Bonus turns, Booms, etc.

B is calculated by adding up the following
- (Cost of jets)*(8% of the jets you have to send)
- (Cost of oil)*(jets you have to send/25)
- (Cost of tech)*(Q)*(tech per acre you want to maintain on the new land)
- (Build cost per acre)*(Q) + a little bit for destroying wrong building types
If techer, include
- (Tech price)*(TPT)*(Turns needed to spy, grab and build the new land)
If not a techer, include
- ($$ per turn if you hit the Cash button)*(Turns needed to spy, grab and build the new land)

You need to be able to estimate Q, the amount of land you would get if you made a grab, and also estimate the number of jets you would need to perform said grab.