I have played TA quite intensively for a while, with my clan mates. It was good fun but gets expensive after a while. I played two worlds, in the first world we were the number 2 alliance, in the second the number 1 alliance IIRC. I choose to "only" invest 5 € per month, but friends of mine invested much, much more.
It's quite decent, but the fact it is so exponential, has as a consequence that it's nearly impossible to actually gain up on someone else. Strong gets stronger.