The real negative to GFFP was that it basically said that the existing population was of no value. The equivelent in Aurora is to terraform away their atmosphere then undo it for your population. I can say from playing the RM in our current game that genocide didn't pay. They genocided one race and after neutron bombing them away put in their own colonists. The system's primary value was that that is gave them some 1000+ free IU. Then with the Beur they landed troops, occupied and have been quietly indoctrinating the population. They are making far more from that tactic then they would have from wiping them out. They also have on the Beur homeworld a medium population (around 500 PU) of indoctrintated Beur and all the colony worlds are over 10% indoctirnated. The more value includes the cost of the garrison forces and the cost of indoctrination. Also with normal growth the amount of indoctrinated Beur would be larger. The adjustment to the negotiation modification is also high.
For Aurora population is always valuable. So nuking them away doesn't really strike me as a worthwhile thing to do. But closing loop holes that allow for easy genocide should be done. It should be an option of last resort rather than as GFFP indicates the first best choice.
In starfire the issue is compounded by the ease of detecting and destroying the defending troops. In reality there was a saying "The Ships the Fool that fights a Fort." In starfire this was not the case. PDCs were easily destroyed from orbit because of the x10 damage from an atmoshperic blast. Moon bases suffered from the fact you could not install shields, leaving asteroid forts as close to the best option to defend a planet...but they can't. To defend the planet the bases have to be far enough out to stop you just firing on it, and if they are that far out they aren't mutually supporting. Once fighters with fL show up the 1LS circle of death can easily obliterate a base for limited cost to the attacker. Put together it meant that defending planets is all but impossible.
And to me that is not good for the game. It basically means that a potential battleground was removed from the game. Starslayer and I had some fun with an older campaign as one race tried to keep the J'Rill away from their homeworld. But if you look at Stars at War you see where the TFNs money is spent...bases defending planets...only mechanically that doesn't work. Once you have fR, fRAM or fRAAM well only PD bases have value but the number you would need to stop small craft/fighter/GB strikes...is hideously expensive. Or...just send in the pods.
To my way of thinking planetary invasions are good things. They are tense and exciting and in all likely hood relatively short. They need specialized assault ships which drain money from building pure combat ships and that is also good. If planetary defences were more effective then money could be usefully diverted there as well. This works to keep fleets managable without imposing restrictions. The more meaningful money sinks a game has the better.
And for all that to make sense you want to keep the value of the captured population high. Frankly the only reason in Starfire to not nuke them from orbit with neutron bombs is that you can get a roll on the intel table and that isn't always useful anyway.
