Another complicated pain is decay.
It was introduced to put a downer on players or whole families saving up too much.

I do think that it is good to have mechanics that put a cap on storing up stuff. Too much savings are not in the interest of the game. As it was said quite often: It's Imperial CONFLICT and not Imperial SAVINGS. And everybody knows the feeling of having had a wonderful round and storming from one exciting war to the next... just to get ripped apart by a family that has stayed out of everything and saved up.

So the topic is not only decay but also how to avoid too big savings which are not in the interest of the game?

Unfortunately there are 2 problems with decay:
1) It's not working as intended otherwise the above scenario couldn't happen.
2) It's complicated enough that one is not able to really calculate wether you'll have the necessary food or minerals in 24h or not. So everybody just builds plenty, doesn't calculate, instead uses approximations. So I'd rather not solve point 1) by just raising decay.

A solution for both problems would be to replace decay with a cap or maximum on how much you can save up. Looks easy, but the devil is in the exact implementation:

a) It shouldn't be a fixed maximum but a dynamic one, growing together with the empire.

b) At first I thought that an easy dynamic savings maximum could be linked with the production. Example: You can store no more iron than your buildings produce in let's say 4 days. But what if you rely on the market and don't produce any iron? Or vice versa: You produce mainly iron and sell it on the market for cash... what should be your max savings on cash then?

Perhaps a better connection would be the number of planets or the overall number of buildings. And therefore it doesn't get too complicated to calculate it, the max savings for each resource: food, iron, endurium, octarine, cash, is shown in brackets behind the presently stored amounts.

As you can see this idea is still in the discussion phase before a poll can be made. I'd be curious to hear other opinions and suggestions about:
I) What would be a good link to calculate the dynamic maximum for savings? Overall number of buildings, number of planets, something else...
II) What should be the max savings, roughly given in days? About 4 days or 7?