For a landlocked nation, diplo points/ideas are mostly useless

[clif9710]

I enjoy taking a small/medium country and expanding. I've played Bavaria and now I'm playing Bohemia. In both cases there is no possible navy until I expand to the coast, by which time other countries navies dominate the sea. The naval perks that come with diplomatic points, and the majority of the ideas available using diplo points don't do my nation any good, though there are a few (just a few) trade enhancing perks.

The up side is I can save my money not hiring any diplo advisors, the down side is I'm way behind the pack in diplomatic points and that keeps the score down.

Since my neighbors are in the same boat (ha! without a navy!), it doesn't detract from the fun of the game. The point could be made that by diverting resources to a navy, a coastal country could leave itself open to attack from a stronger inland power.

[Free Luigi M.]

This is only a problem when it comes down to game score though. Since navies count as diplomatic score.
The fact that not all ideas are viable for all nation is natural and only logical. In any case Diplomatic and Expansion ideas are both good choices in the diplomatic group for landlocked nations. I am in the middle of a Brandeburg game and the first idea I picked was Diplomatic.

[Brasky]

Yes, diplomatic ideas can actually be quite useful. I overlooked them when I first started but as I play more the +2 diplomatic slots and +5 diplomatic reputation is very helpful for the old fashion diploannex expansion strategy. And some landlocked countries, in the HRE for example, diplomatic ideas is almost essential.

[Korburss]

Diplomatic is probably the number two idea for any nation in the HRE with only Religious and its 50% better relations beating it out. Also as Joe pointed out. A perfect storm in the HRE probably involves Religious, Diplomatic, and Expansion. Together you get +4 Relationships, +8 Diplo Rep, and +50% Relations over time. Then throw in the HRE Emperor bonus of +2 Relationships and you match the number of relationships Austria gets with all NIs presuming they don't get Diplomatic ideas.