Influence has always been a blobbing idea set, from the moment it was added to the game. The whole group screams vassal-feeding. It gets even more crazy when you consider the Administrative-Influence policy (and Influence-Plutocratic to a lesser extent), and Religious-Influence policy also has great synergy if you like culture-converting (Manchu countries and so on). Certain countries could try to stack AE reduction really hard by including the Innovative-Influence policy. The other policies are mostly nothing special.
As I understand it, Diplomatic is a popular option to take early for the game of thrones (due to no stabhit for breaking royal marriage, and the extra diplomat comes in handy), but if you're not a Christian monarchy it generally takes a back seat to Influence. I suppose it could feed into a hyper-aggressive style, with cheaper trucebreaks/no-CBs and ability to take more land in a single war, but probably more conventional blobbing ideas are a higher priority even in that situation. In terms of policies, there's a +diplomat policy and a ton of diprep ones (again, great for game of thrones) and Diplomatic-Defensive lets you pay for a diplomatic relation with sword mana, which is quite handy.
Espionage quite a mix of different things, all of which are somewhat helpful but none of which are individually outstanding, so it's hard to know when to use it. Maybe more fun for role-players than power players. I think it has some potential for countries that are going tallish (you aren't taking your enemies' land, so you want to disrupt them by other means). It could do with a finisher of cheaper spy actions (i.e. so that you need less spy network to steal maps, agitate for liberty etc); rebel support efficiency is a bit too specific, and all it really does is make the rebellion fire a bit faster. The policies are mostly for players who want to create an early modern CIA for some reason, although Espionage-Quantity is somewhat interesting for countries that use a lot of mercs and a couple of the others give nice military buffs.