Right now in Diplomatics you can buy nearly anything for Diplomatic Capital. If your enemy is a really diplomatic badass having 2000 Capital while you have a meager 150, it seems strange that you can throw your Capital to decide deals, neglegting his superior Negation Power. This allows, e.g., to simply buy technology from vastly superior AIs for cheap Diplomatic Capital.

I propose, that if Diplomatic Capital is offered  to sweeten a deal, the Negotiation Partner also automatically throws in his diplomatic Capital, up to your value. So this means, that you need to have more Diplomatic Capital than your Partner to make him accept your Deals by this way.

Furthermore, no deal should be struck for only Diplomatic Capital. E.g., Tech for diplomatic Capital. Some "real" values should always be involved.