Seems sort of silly that when I create stores in my settlements I can't invest in those stores. The entire idea of creating the stores was so I wouldn't have to wander God's green, irradiated Earth trying to sell all my drek. Seems like this would be an easy fix. *shrugs*

What do you mean you can't invest in them? You can just go sell stuff right to those stores.

He means invest by increasing their total available caps with the perk

Yeah, I have some up to 800 caps and some up to 4-- caps, but I don't get an invest option for the extra 500 for a one stop shopping kinda deal. Sorta silly I can't invest.

Might be a bug, I can't see why they would have intentionally made it so you can't invest in shops in your settlement, after all IT'S YOUR OWN SHOP FOR CRYING OUT LOUD!!!!! If you can invest in shops in the middle of nowhere in the wasteland you should be able to invest in your own shops in your own settlement.

Definitely seems like a bug to me.

Come to think of it, the last level of the Local Leader perk does explicitly say that "you can now invest 500 caps with vendors" or something along those lines. It's possible that this is some kind of glitch, because I didn't see any change after getting that perk.

edit - A quick search led me to this Reddit post.

https://www.reddit.com/r/falloutsettlements/comments/3tkh62/how_to_upgrade_your_shops/

They're basically saying the when you go to the barter menu, there's an option to "Press Q to invest."

And I just stopped in the middle of typing this post to check, and the option is indeed there. I just invested 500 caps with Anne Hargraves, the legendary clothing vendor. I'll do the rest tomorrow. Open the barter menu and there are all of the different options along the bottom below the inventory screen. The last option is "Q: Invest" If you're on console it'll obviously be a different button, but it should be there, assuming that you have the Cap Collecter 2 and Local Leader 3 perks anyway.

So there we have it. You can invest an additional 500 caps into each of your stores. According to what I'm reading, you can also invest 500 caps with Trashcan Carla and the various merchants at Diamond City, Goodneighbor, and wherever else. I'm about to head to bed but I'm going to have to look into that tomorrow. I've got enough caps to invest in every merchant I visit regularly and still have tons left over, so that would be a worthwhile investment with my water farming and mass-production of Jet.

It's the last Caps Collector perk.
I suppose I should go hit up Arturo.
That man owns an apartment complex in the Upper Stands with all the money I've spent in his shop.
My immediate response to levelling was heading back to Sanctuary and all my upgraded shops and no options.
Also, Trashcan Carla's Brahmin is on my roof with Mama Murphy.
So Carla never leaves. Ok cool.
And I convinced Mama Murphy to cut out getting high on chems.
And now she's high on the roof.

Did you see my edit above? I just now invested 500 caps with one of my vendors.

What is the tangible benefit of the last level of the perk? Does the inventory get better or their average amount of caps to trade with get higher? I know the perk description says it's better, but by how much?

They just have more caps available to barter with after you invest. There's more caps to be made and less "I'll trade you 30 pipe pistols for your shogun shells and a couple missiles." Only use it if you just want more caps in your pocket for expensive items like ballistic fiber shipments or whatever.