1. Wilderness encounter tables (since they weren't in DMG).
Disagree. Never use them, and they take a lot of place. IMHO, this is the kind of stuff that is better as a web-enhancement. This way, it may be updated easily; especially if presented in an HTML form -- it may even be imported into a spreadsheet then.
2. An entry for Humans, like the ones for Elves, Dwarves etc.
Agree. Also, for most humanoids, provide also a statblock with the favored class rather than the default warrior. And a sample of a level 3 or 5 character that could be used as a leader for a mob. And an ECL given for each creature having a *Thingie* Characters section.
3. The rest of the missing monsters from the 1e Monster Manual.
I would tend to agree, but I would need to know what they are.
3. Death Knights, & various other classic monsters.
Agree. Banshee, death knight, phenix, in particular. The dragons from Monsters of Faerûn, and the yellow dragon as well. And finally, the damn lupins and rakastas. They're as valid as gnolls and lizardfolk.
Somehow, I think that the Monster Manual should not be 360 pages, but 720, and be really, really, full of beasties.