Don't know if this will help but you could try running Gnome with another window manager instead of metacity.
A week or so ago I decided to test Gnome (in Debian Etch), wasn't happy with metacity and replaced it with XFCE's window manager xfwm4. In the end, I didn't like Gnome enough to keep it but here's how I switched the window manager for Gnome:
(1) First, I installed the "xfwm4" and "xfce4-mcs-manager" packages.
(2) Then I edited /usr/bin/gnome-wm, making the DEFWM line to look like this:
(3) Then I removed my saved Gnome session file ~/.gnome2/session so that it wouldn't override my changes in /usr/bin/gnome-wm.
(4) After starting Gnome with xfwm4 as the new window manager, I adjusted the xfwm4 settings by starting "xfce-setting-show".
As I said, the above might not be what you're looking for but it's the only suggestion that comes to my mind at this time. Hopefully someone who regularly uses Gnome can offer you better suggestions but Gnome is notorious for not being very adjustable, so don't expect too much. It's possible that one just cannot tweak window resize animations in the Gnome+metacity combination.