I wouldn't go that far. If you're confidently swimming in DIP, go over #relations to expand more rapidly.
I've never found dip relations to be a problem, personally. I find the annexation penalty on vassals to be a far bigger limitation if I can't return cores.
If you're that far over in ADM, add coring to 100% or more OE on top of that.
Coring times are so long for a large empire that it's more practical just to completely annex a country w/o coring then release them generally. Use adm on stability after breaking truce if over 100 OE, but thats about it, and that's only if no one will take their provinces.
Even culture converting > sitting at 999, but in reality that's usually bad too.
As I think you were alluding to, the return on investment isn't very good. At that point in the game a marginal amount of tax, manpower, and RR aren't going to make a difference.
Military is harder to avoid going over on, but you can generally compensate that by taking more idea groups in that category.
There's still large periods of time in the end game where you'll have capped out an idea group but not be able to start a new one. A single idea group costs 2800 monarch points, and will be spread out by at least 4 techs, 52 years, which has a base cost, as western, of 2400 points. Thats 5200 points in 624 months, or 8.3 points per month. That means a mediocre to average leader will exceed the amount of military power you need with a +3 advisor. The gap between the 5th and 6th group is worse, because it's a 5 tech spread so you only need ~7.4 power per month. This is assuming no research bonuses, which is frankly pretty unlikely after 1600.