I find it very odd that the AI tends to hoard money. I usually play on "king" and already in the early 18th century some of the "fat cats" already own 50.000+ gold. I'd suggest to implement economic mechanics like inflation, that is activated after a certain tech is researched (maybe economics). A possible realisation of this idea appears to be quite easy if the inflation ratio increases proportional to the treasury and the particular "GDP". In fact, the bigger the specific treasury is the more the national income shrinks until a certain value is reached (which depends on the GDP itself (richer nations = bigger treasury)). Such principles would make the whole thing a bit more realistic because absolutely no "industrial" nation would have any interest in hoarding so much money instead of investing it.