What to do with all this gold?

I'm having a lot of fun playing Ottomans in EU4, I've gotten up to around 1630, got 110 provinces, and my economy is rather awesome. I have a surplus of around 150 ducats per month, and I'm running out of ways to spend it. I spend a lot on building out my provinces, but since all buildings cost monarch points (adm/dip/mil) as well, I can't just spend all the money there.

I suppose I could use it to hire all available mercenaries, but my 134K strong army doesn't really need reinforcing.

Using it for improving relations could be attractive, but it seems no matter how much you spend, you can never get more than 15 relation points, and I tend to get that with just 25 or 50 ducats.

I've hired all level 3 advisors, to try and convert some of the gold into monarch points, but I'm still running with a huge surplus.

So now I'm just accumulating money, got over 30K in the bank, but that just seems wasteful.

Any suggestions on how I could use some of all that money to further my quest for world domination?

After a certain point, money becomes virtually useless. The only thing you can spend it on effectively without using ruler points is mercenaries, and since mercenaries cost exponentially more as you go over force limits it starts to be a waste.

In EU3 the massive money sink was the ability to spend gold to gain technology. Now that EU4 has removed the ability to do so, so your gold is pretty useless.

Build Buildings, mainly military, naval, and production. Higher production means more manpower, better navies allows you to dominate in wars, and military buildings lets you recuperate from wars and fight better in said wars. You don't REALLY need to build the other buildings because you have a pretty penny already. Also, do not forget that buildings also cost monarch points!