I am not going to talk about the metal extractor or power plant. I would like to talk about the profit of PA:Titan. My motivation comes from other games. I also play other free online games such as world of tanks, and I pay the money quite often. But the PA:Titan is totally different, once I pay for it, I get everything needed in the game. Thus, there is no more purchase. Even I love this game so much, I have nothing to buy. (Commander avatar? I already bought one. ) Maybe Uber can use the concept such as the bulletin of Company of Hero 2, or the weapon of Team Fortress 2. Players can collect some elements for free if they play the game with enough time. Or players can buy it immediately. Players should get some default items with enough strength, and the gathered replacement items should not be overpower. Thus, PA won't become a pay to win game. Keeping adding new items can make the game fresh and long life. The collectable items for TF2 are the weapons. For COH2, the items are bulletin, and special units/ability of doctrine (commander). For PA, I am not sure what can be the collectable items. Perhaps they are bulletin and commander upgrade? For bulletin, it can be vehicle sight range +2.5% likes other games. For commander upgrade, the commander has 5 default equipments: anti air turret, main gun, uber cannon, torpedo launcher, T1 fabrication tool. Maybe in the late game, player can drop some of them and replace them with other equipments such as anti orbital turret, tactical missile launcher, T2 fabrication tool, self healing or personal shield. The collectable items should be useful, not overpowered, and they should always comes with some drawbacks. I think they are better idea than the next expansion since they are smaller and easier to publish.
i don't quite understand the OP are you asking for unlockables through playerprogression like in COD?
What about paying for faction skins? Same stats and play the same but look different or wacky. Or DLC biomes for that only the host need. I think a sugar rush type biome would be cool.
Settle down now, the last thing this game needs are players engaging in tense trade discussions during a competitive 1v1. Think of the un-microed Dox. Think of the leaderboards: "I'll give you my uber position in exchange for that deluxe super conducting hat" "Sounds good, I was getting tired of being a skru.. bronze 2"
Different skins could be just for one unit. For example you could buy cooler skins for your favourite unit, boom bot. It would scare your oponent.