The Iranians have a plan. There are many excellent upgrades available for older tanks, and they want access to the European firms that do this work. The largest assortment of upgrades are available for the Russian T-72 tank. Iran has about 900 of these, of several models from the 1970s through the early 90s. The next most common tanks are nearly 600 T54/55 T-59: (a 1950s design). Upgrades are also available for this one. The rest of Irans tanks are an odd assortment of vehicles not present in sufficient numbers to do upgrades. These include 75 Russian T-62s (not much better than the older T-55), 100 Shir Irans. These are locally developed, from the 1970s project based on the Chieftain (1960s vintage British tank). There are also 150 American M-60A1 (1960s era tank), 168 M-47s (1950s era American tank), and 100 Zulfigar (a locally designed tank, not as good as the T-72).
The principal upgrades are improved fire control (computerized, with laser range finder), more armor (ERA, which is explosive reactive armor) and better ammo (the Chinese even sell depleted uranium shells). Improved communications gear is another useful upgrade, as well as new engines and the replacement of many other parts that have worn out after two decades of embargoes.
Iran often talks about, and acts on, efforts, to build its own tanks. Two efforts at this have been dismal failures (although Iranian media said otherwise, professionals in the Iranian, and foreign militaries know better.) Buying new tanks in any quantity is not possible, but upgrades are. With these upgrades, Iran will dominate most local forces. Only the United States, and its thousands of M-1 tanks, would remain a threat. But thats what the nukes are for.
One reason Iran, despite its attempts to create nuclear weapons, wants to make nice with the European Union, is so that the Iranian tank force can be upgraded. Currently the Iranians have about 2,000 tanks, all of them rather out of date, poorly equipped and not in the best of repair.