"The M1 is good to go, as is. The only improvements that should be made should concern themselves with mobility and protection (other than cupolas and gun shields). Not firepower." 
Yes and no. Yes to the extent that the M1 series is the reigning world heavyweight tank champion. It kills all other tanks dead.
But "no" in the sense that a lot of our War on Terror missions are no longer against other enemy *tanks*, but against enemy personnel in urban environments (think Najaf, Fallujah, Basra, Baghdad, etc.).
Moreover, we've got some 2,300 M1's that are mothballed, unavailble for our use because they are officially "obsolete" with their 105mm main battle cannon.
Please keep in mind that we have 3 prime variants of Abrams tank: the original M1, the M1A1, and the M1A2. Of these ~~ 7,000 U.S. tanks, around 2,000 of the older M1 original variants are off-limits and parked in the States.
I'd like to see those "obsolete" units upgraded into a vehicle that could support our current urban warfare operations (e.g. in Najaf).
For such roles, the upgrades in demand would be those options that enabled greater "staying power" (e.g. 4 half tracks instead of 2 treads) and better infantry support (e.g. with the A-10 ground attack fighter's great GAU-8 30mm gattling cannon).
Then I'd like to move them out of the States and into places like Iraq and afghanistan where they could make the Iranians nervous.
5 Legislative Days Left Until The AWB Expires
Gee, and a 105 mm gun wouldn't be useful in a short-range knife fight like Najaf? They may be classified as "obsolete" for tank-on-tank combat, but they would probably do some good in urban combat. Again, the question is NOT whether a tank can be adapted to fight in that type of enviornment, because it certainly can, although many of the changes needed to make it "invulnerable" in such situations would make it incapable of carrying out it's primary objective: taking out other tanks. The question is "Is a technological development necessary to make such operations safer for our troops?". The answer to that is NOT a new tank or a new vehicle, or perhaps even new technology. The answer is in better (perhaps more brutal) tactics with EXISTING weapons systems.
I could give a rat's behind about how many dead we leave behind in street fighting in Najaf, so long as they weren't AMERICAN dead. To do that you flatten the place and return it to nature. You do not spend several billion dollars on new tanks. Money that would be spent on the upgrades/changes you suggest would be better spent on research on the next generation of MBT's or perhaps in better training/prtoection for our infantry (of which, we are critically short).
The current "War on Terror" missions you're talking about are not difficult because we lack a killer weapon, but because we lack boots and the stomach for dirty fighting. If you think differently, I remind you that there have been at least 3 cease-fires in Najaf and the other side has used the time to regroup before attacking again. New tanks do not solve that problem. Destruction of the enemy does.
It's a different mindset that's required.