Very good point. it will affect even more once people start moving to digital age. since entry level is 285. any digital age base in mp will be hard. to reach 285 you would have decent defense. though it balances wars. multi player battles needs some balancing. giving away more NTG's via dialy shipments or victory chests is a good way. reducing time on these dock shipments with new library or university upgrade is also a good thing. at present in 3000 to 3400 medals you get 3-4 NTG. this is very less compared to the medals.
Ug to DA will only change that Cold War bases will be smashed more easily with DA offense. The increase to DA might be less as many think. Atm there are only 2/3 active players between 275 and 284 as already are 285 or higher. And reaching 285 is a pain in the ass, 10 to 13 days for one level.
Introduce a new building (or use an existing like storehouse or command post) to offer trading of NTGs.
Take the original Marco option of trading in 3 of one type for 2 of another but make it a much wider scope facility so that there is always an opportunity to trade for the type you need.
It will always be really tough to make all nations equally appealing at every age.
It will probably spoil multiplayer to open up all Vs all attacking (although I do think MP battle rewards are nonsensical right now). You could open up attacking to all but you need to incentivise players to want to hit high, and the incentive isn't big enough now - mainly because of NTG requirements. There's also the manipulation of the new event system to consider, if high end players can hit baby bases it might lead to these bases getting hunted.
Having a comprehensive NTG trading post feels like the way to go.
Please excuse me while I return to hitting Next until I see porcelain...