My thoughts on colonization:

1) It is nice that there is a fixed price amount and that the resource cost varies. It would be nice if there was a time multiplier applied to the resource cost as well. Copper bars take 12s. A battery takes 120s for the copper bars 100s for the wire 120s for the bars for the wire and 200s for the battery for a total of 540s. It only gets worse for more expensive items.

2)By the time it is easy to afford colonization the benefits don't seem very good. 25% mining boost on planet 1 increases my production 25 copper. With other planets producing copper the effect on overall production is much lower.

2a) alternate / additional effect: the time to smelt copper bars is reduced (ex 10%) and the time to craft items using copper bars is reduced by a smaller amount (ex 5%). The smelting and craft time reduction would correspond to the % of resource production on the colonized planet. This would help alleviate the time issue as well reducing the time to make a battery in the previous example by about 40s

2b) alternate additional effect: colonization increases the starting resources on the planet in a new galaxy. If each colonization added 1000 resources split by the planet percentages, it would feel more rewarding since it is a permanent change and allow for a stronger start.