Dyt's idea is really good. Metrex's idea is intriguing. Aiding allys could be overpowered though. It would have to have restrictions.
make it take time to arrive from one family to another. Calculate the distance between homesystems at 20 (possibly 40?) speed. Game terms they would be space freighters. They should be faster than a DS. Maybe it only functions for a leader, fa and vl. Giving only, or perhaps both giving and recieving. A leader would have to be careful with the VL tag cuz it would give them more power.
Instant aid would make the start of rounds insane. The alliance could easily make a superbanker fast. My idea slows it down a bit and forces the alliance into thinking about coordination and timing. You could also prevent alliance aid the first 48 hours.
it would be neccesary to keep track of a family's 'credit score'. Calculate how much they gave given and recieved in cash and resources. You would have to assign a base value to each of the resources + cash and have it be one total. It would be unfair to publish exact numbers. then everyone else knows too much. You would have to use a bar and make it more ambigous. You start at 0 in the middle. Red negative, green positive.
You need to see this 'credit score' to avoid the bad guys out there who are only switching allys to leech off them. You gonna ally the family with a huge red bar? The one who just dropped their ally and now wants to ally you? If you leave this debt a secret your gonna see alot of dirty moves. Family 1 of the alliance takes loads of aid and drops family 2. Family 2 posts in uni about the theft. Family 1 denies it and calls Family 2 liars.
Which raises the question.... how much do you trust your ally? We all witnessed numerous alliance changes in this current mw round. do you really wanna send your family's resources to the ally who may drop you for someone else the next day? Scary.
So will alliance aid actually improve gameplay? Adding another element to relations and diplomacy? Or will this simply be another way to screw over a hapless family and use them for resources. Perhaps making it more cut throat? Im not exactly for this idea or totally against it either. Im just playing devils advocate. Ally aid complicates things 
Ultimately though it comes down to wether or not Ps can do this. Could be overly complicated.
The path of the righteous man is beset on all sides by the inequities of the selfish and the tyranny of evil men. Blessed is he, who in the name of charity and good will, shepherds the weak through the valley of darkness, for he is truly his brother's keeper and the finder of lost children. And I will strike down upon thee with great vengeance and furious anger those who would attempt to poison and destroy my brothers. And you will know my name is the Lord when I lay my vengeance upon thee!!