#1
Okay,

Well, I bought my new Hagstrom after my horrific accident early last week, and the pickups sound GREAT. Much better than the Invaders.... (these are Custom 58's)

Would switching to ZW EMGs be THAT much of an upgrade...???
I've bought, sold, and traded more gear than I care to admit.
#2
Not that much. More so just different tonal characteristics, not more output.
Framus Cobra
Marshall JCM 900
peavey 5150

Mesa 4x12
#3
the output would go up and your tone would change significantly. For better or worse? That's realy up to interpritation. Some people love EMG's and swear by them, some curse their name and bash them at a moments notice. I'm in the middle, i like them enough to have them in two of my axes but I know that there is a huge amount of pickups out there and I have different ones in each of my other axes.
Out here you've gotta know where your towel is!