From: Republic of Cascadia
Very interesting points made here, but I personally feel it is fine as it is. I can summarize a few things about my opinion:
1) The Entente I feel should have a larger diplomatic gravitas simply because they have a larger footprint on the world. While that may sound simplistic, the fact is economic resources and monetary power is a foundation of diplomacy, not just smooth promises and big gunboats.
2) I don't feel increasing diplo chit expenses because all of them have been dumped in one country should be penalized. In fact, as you already perceived, spreading those chits out incrementally over time can have bigger returns and can fool your adversary (at least a human) into thinking your going in one direction than another.
Example a): Lets say the CP has 2 chits in Holland, 1 in Bulgaria, and has 2 not bought. Your opponent, (if he reads the reports that is) will see over time that 150 mmp has been spent..a few turns later, the German player gets lucky and that 5% chance chit pops on Bulgaria. Now the Entente player may think hes dumped it all in Bulgaria, and try to counter..instead, for the German, it doesn't matter..Bulgaria is already on the high road to joining the CP because the Serbs are being ground down into defeat, and Holland isn't bothered by the Entente spending money to influence The Hague.
Example b): The Entente player really needs Romania to join their side..and has has spent some modest mmp's into it for a year with some gain but not what is desired. So the Entente player, via Russia, knowing that the taking of Lemburg (which they took earlier and saw the message noting Romania's 'Interest'), then plans an offensive to take Przemysl and Crakow. The Russians understand that their own losses will be high, there won't be spare money for any diplomacy until these two objectives are taken. (which the Entente understands will trigger positive pro-Entente percentages). So, while the operation is in progress, other Entente members (and Russia if they can afford it) take a calculated risk and dump en masse mmp's into Romania, an expensive enterprise. Timing was important here, the desired result is achieved e.g. Cracow and Przemysl taken, Romania gets bumped pro-entente beacause of this..a few turns later or concurrently, the diplomatic chits start paying off, and Romania is at 92% pro-Entente and is going to join the slaughter.
3) Diplomacy chits are expensive enough and they compete with other necessary and critical needs that have meaningful and quantitatively known outcomes for the economy and the military. There are still some probabilities involved that can make the next threshold in a research line achieved not perfectly known, but its less squishy then diplomatic investments and outcomes are, especially when opponents maybe trying to monkey wrench your efforts in that space.
4) Deciding when to spend MMP's on Diplomacy shouldn't be taken lightly, and should be regarded as an adjunct of the wider strategic situation as it unfolds. I don't believe focusing massively diplomatically on one country should be 'nerfed' at all, as while that strategy may seem optimal, in fact, it could be a money dump that weakens the country(s) participating in such an unsophisticated manner. And sometimes, in my opinion anyway, in this cold hard world, money equals power and should be used as a blunt instrument when more subtle means aren't working.
Of course, these are just my opinions and this could be wholesale rubbish