upgrade to 12.04 LTS vs fresh install questions

[Linda]

I have several machines that I can upgrade from 10.04 LTS or 
just do a fresh install to move to 12.04 LTS.  In making my 
decission on whether to bother trying to upgrade to the new 
version I was looking for opinions on two questions?

1. the 10.04 LTS have ext3 filesystems, is it worth the 
extra effort to do clean install and format the drives with 
ext4 file systems?

2. Some of these machines do not have network manager on 
them for 10.04 LTS as all the network configuration was done 
by hand. I did a trial update on a machine I had replaced 
with a new one and the upgrade to 12.04 LTS installs 
network-manager but  it gives an error that it is 
incompatible with the current version.  I removed network 
manager but you can no longer create a resolv.conf by hand 
as it rewrites it at boot. I tried installing 
gnome-network-admin to set the dns nameservers but it still 
losses the nameservers on reboot. Would installing 
network-manager on the 10.04 LTS machines before upgrade 
eliminate this issue?

               Thanks
                Linda