Channel subscribes are public for reasons I don't totally understand myself. But I've only been on the network for a while, perhaps old-timers can help you understand better.

As far as content goes, so far what's worked for me is:

1. Following a bunch of pubs + interesting people.
2. Using #patchbay, which fetches messages further away from you (i.e. you'll get threads not from your friends or your friends' friends, but even further away on the network).
   2.a. Every time I fire up Patchbay I get a nice batch of messages, some from years ago, some from recently. The amount of data I'm pulling in may not be sustainable long-term, others have talked about cutting back on follows; I'm not at that point yet.
3. Subscribing to and browsing channels I'm interested in.
4. Searching for keywords I'm interested in and following the rabbit trail.
5. Looking at the weekly digest that gets put out with links to interesting threads from the last week. Most recent one is %rU55MNp...

I believe this is due to 2 things @lil coldy.

1. Hops

Patchwork & Patchbay might be using different amounts of hops in their configs. Hops means the number of jumps your system will go. so with a hop count of 3 (which is the default on most devices and services) you will get gossip from the people you follow, the people they follow and the people they follow.

2. queries

Patchbay and Patchwork both run "queries" (a fancy term for requests for data through questions) on your local database. Patchwork seems to be a bit more careful with its queries on your database and show less wild messages from friends of friends unless one of your friends likes or shared in the discussion. You can see more extended networks in both apps though by going to the "extended network" view.
Some word of warning there is that though you are receiving their messages, replying to them doesn't guarantee they will see your replies.

Word of warning when using multiple "ssb-apps" on your machine, make sure you only have one open at a time. Patchwork will want to insert new messages into your database when it sees things coming in, if you have a second app like Patchbay open you run the risk that they both get a message and will try to insert new things at the same time (causing collisions and a whole lot of bad shenanigans). so Close patchwork, wait a few seconds for things to cool down, then open Patchbay/Patchfoo/whatever. ;)

Some great content of visualization on the network and how these 3 hops of friends look for me: %A1mT76p...%A1mT76p...

(or ssb.picoreclame.nl)