I will skip all the individual points and just go with a single response, if you are buying T-55-T-72s you are buying them for regime maintenance not to fight a war with anyone that can spend a couple of mill on ATGM's and about the same on some clapped out old Russian Mil-24s.
The fact is that short of the latest model Russian tanks all the previous models are little more than cans of pre-cooked meat to anyone wielding more than sticks and stones.
You do realise what a challenge it is to hit a tank with an ATGM and destroy it? Oh wait your knowledge comes from computer games, also you realise any army will be OUT of ATGMs in the first week of the war and only some of the will be used on tanks?
T-64's and T-72's have such crap FCS that they would not even be able to accurately return fire to an upgraded or modern MBT like the Leo 2 or M1A2 Abrams, hell an upgraded M60A3 MBT even. If you wanted to get the models of T-72 that actually have decent equipment like ERA or a decent FCS, they would be more than likely out of your budget in this scenario if you wanted 400 of them.
I COULD be rude and call you an ignorant moron but i feel charitable, since you are an ignorant moron i'll even help you quite a bit.
T-72B has a 20+ years fire control system 1A40-1 and 9K120 giving him the ability to shoot ATGMs, now explaining how the afformentioned systems work might overheat your empty skull and if you do some research you might refrain from issuing moronic opinions.
Suffice to say T-72B can frontally gut M1A2 from 2000 meters using an ATGM.
As for upgraded M60A3 will not penetrate later versions of T-72s and T-64s frontally unless its using an ATGM, while a single shot (depending on the ammunition) from any of these and including later T-55 models will leave the M60 of any variant as a smoking wreck.
The point about T-72 is that with the works its still cheaper than 2A4s or 1A1s even, i got a table (its in german though) with price comparison somewhere if you're interested.
The only real problem with russian tanks to date were the crews or export versions but the countries of the former Warsaw Pact have both technologies and ready machines to sell upgraded machins at a reasonable price.
To put it on laymans terms, an upgraded T-72 is a rough equivalent of a Leo2A4 but at least 40% cheaper, that makes it a good choice in any circumstances.