Yes, yes it does. Whether you pay with money or with investment you still have to pay your current stabcost. Sure, If you get a stabhit for say, DoW'ing a country without CB, and then pay off the stabcost before you get the infamy hit from annexing them you lose a bit of cost, but not nearly enough. In that case its probably worth it to just occupy that country for a year and wait for your stab to raise from investment.Because it doesnt limit my expansion into foreign territory.
But thats only if you are at 0 RR and not the typical (-10)-(-14) RR you can usually aquire. So usually you only get say, 4 RR at most in most core provinces.+3 stability gives:
[List of cost]
Each revolt risk point decreases taxes by 5%, so altogether, the +6 RR from negative stability, may decrease taxes by 30%. Legitimacy decrease is also bad here, but you may keep it unimportant with enough royal mariages/other modifires. If we count the reduction being lowered, it might mean even 45%
We are talking about a -6 Stabhit here. That means the alternative is ~6 Inflation. But look at it: Even with those kinda inflated numbers you still wont even lose 50% of your income. Lets go by the (reasonable) logic that 40% of your Income is Trade, 30% is Taxes and 30% Production. Lets say that the merchant stuff costs you half your trade income (unlikely, but it defnitely wont cost more). You lose 20% income. Then you lose 75% of your Taxes, which means a reduction of 22.5% of your whole income. All in all that still leaves you with an reduced income of only 42.5%. That means that in addition to the lots of ducats minted you still lose. Even in the most extreme case of a -6 Stab hit. As long as the stabhit does not bring you to negative stab its a drastically changed story, do the math.So the difference is:
up to 75% taxes
6% compete chance
up to 6 merchants
So the only thing not affected by stability, is production. Unless you got very high production, and low trade and taxes, i think minting to be able to quickly return stability to maximum, might be a very good idea.
If someone declares war you will actually get a -5 RR modifier in your core provinces, while your morale should be entirely unaffected by stab. If you cant pay your military thats another thing.Paying the stabcost is not really a big deal. Having a large empire and a minus stability might mean lots of pesky rebels, and if you are -3 and someone decides to declear war then it will be even worse as nationalistas will pop up everywhere and your forts will have terrible morale.