I am starting, although no one knows who I am
And I can list the points on which the premium features do the biggest difference(just common sense, not using them myself
Getting the smithy up the last 5 or so levels, getting up the farm the last 5 or so levels, and the stable
Not caring about what res you get in the start(not picking farms early) as you can change the res between wood clay and iron
Buying flags is what the top accounts on w68 did(as you will be almost short on flags after a while)
Then later on in the game, the extra res production is actually the strongest of the ones, when you don't farm as "much".
At least the norweigans saved us from one thing:
On one norweigan HP, they experimented with you being able to trade your res(the market thing) for like a 0,7 ratio. You got more res than you gave. However, someone abused it as hell(got to 5k points when rank 2 had 600) to show innogames that they should never think about that again.