I’m interested in running a “Red Dawn” kind of hometown insurgents campaign
Yes. This will definitely do the trick.
Personally I was positively suprised how generic it was. I was expecting a bit more of a detailed look at Krakow/Karlsborg, but the materials devoted to those two cities are just a tiny part of the book and even those can easily be converted to work in any other city. So it definitely is more of an "urban sourcebook" than Krakow/Karlsborg sourcebook. Think of those two as examples for Referees on how to expand campaigns in cities.
Does it have scavenging tables for various sites
No. But it does have new encounters that are for urban enviroments. The cities are pretty much scrapped clean a few years after the bombs dropped anyway, so you probably don't need a "pharmacy" scavenging table and "fast food joint" scavenging table... Then again should you need, the internet provides plenty, even geared for TW:2000.
Does it have details on how urban environments decay when infrastructure collapses?
It has a very rich flavour text in the beginning about what life is like in the city a few years after the war. This style of giving info is present in other parts of the book as well, like scenario site details etc.
The first chapter explains in very informative way what is the likely outcome with food and water, security, laws, economy, transportation, jobs, politics etc. The "decay" of the city itself depends largely on whether it was hit by the nukes or not or did it come under heavy artillery/missile fire during the war. So those details you have to work out by yourself, the book paints with a broad brush, but the picture is enough for most referees.
Personally I am very satisfied with the materials. The city rules for combat and travel in the cities are good (not too crunchy and present interesting choices for players). The plot points were exactly what TW needed imo as well. The scenarios sites are very good and universal.
The only thing I was hoping a bit more from was the faction rules regarding areas of control. While I wasn't expecting "Stars Without Numbers" or "Blades in the Dark" treatment of factions and their machinations, the rules here could have been expanded a bit further to give the Referee more tools into running a living, breathing sandbox. Then again many GM's prefer to run the factions simply by GM fiat which totally works fine, especially with the plot points, so depending on your style this might be a positive or a negative thing.
Bottom line: if you run TW:2000 and your PC's have a slight chance of making it alive to a city of some sort, you definitely should buy this.