So, is the whole Rise & Fall of the Shi'Ar Empire and Kingbreaker series worth reading?
Yes! I loved the entire run. Here is the reading order:
Uncanny X-Men 466-471 (End of the Greys) This isn't Vulcan related as much as Shi'ar related so it's a good prologue and ties in later.
X-Men: Deadly Genesis 1-6
Uncanny X-Men 475-486 (Rise and Fall of the Shi'ar Empire)
Emperer Vulcan 1-5
X-Men: Kingbreaker 1-4
Secret Invasion: War of Kings Oneshot
War of Kings 1-6
War of Kings: Who Will Rule? Oneshot
I'm behind on my Hulk, mostly because I keep hearing negative things about the current Hulk runs, so out of curiosity, is World War Hulk worth reading?
I enjoyed WWH, and there's been some complaints on Red Hulk but for the most part I've found the Hulk line to be fantastic. Now is the only time I've ever actually really enjoyed it. I've found it to be amazing myself, with a few hicups here and there.
I like the Red Hulk stuff myself but it's not for everyone. Dodging some of the Red Hulk stuff and only including what's necessary I'd suggest reading:
Planet Hulk
World War Hulk 1-5
World War Hulk: Warbound 1-5 (not necessary but is referenced a lot)
Hulk 1-6 (Red Hulk and other important reasons)
Skaar: Son of Hulk 1-12
Incredible Hulk 600
Hulk 14-17 (Important for Red She Hulk's introduction)
Incredible Hulk 601-605
Hulk 18
This is what I'd recommend for hulk post WWH, though there's more you can read if you like that becomes a factor later (Son of Hulk 13-17, Realm of Kings: Son of Hulk 1-4, The All New Savage She-Hulk 1-4, Hulk 7-13) but for now you can dodge that. The Son of Hulk stuff post Skaar comes up right after the above listed so it's up to you if you want to lead into that.
After Hulk 18 comes Fall of the Hulks and World War Hulks, which go back and forth between Hulk and Incredible Hulk. The Inc. Hulk issues are fantastic and the Hulk issues are medicre. After that I dropped Hulk but I hear Parker's done a good job with it. Incredible Hulk has been fantastic though
Are there any really good modern Avenger stories worth picking up? Again, I keep hearing negative things which makes me hesitant to invest time and money them.
Post Civil War... it's hard to say. It'll all roles one into the other so just picking out specific stories is hard, and a lot of people aren't fans of Bendis's run. I do recommend Slott's Mighty Avengers (issue 21-36) and the entire run of Avengers: The Initiative. Those were both on the side of the core Avengers stuff but VERY good.