Actually I envision them being the near perfect replacement for Iran's F-4s when their airframes finally reach the point beyond overhaul.
More or less, the Su-24 is the perfect successor to the F-4E. It doesnt have the F-4 air to air capabilites but these abilites are largely non-existent today since the only BVR missile available for them is the AIM-7E who range is compared to a R-73 and has one of the most combat records ever for a BVR missile. So as time passes the F-4 was become a 'bombtruck' of sorts whereas the Su-24 was originally designed for just such a task and is naturallly better equipped for the task.
For example, the Su-24's avionics are designed for not only medium to high altitude strikes as the F-4 was designed but for terrain following strike missions under the enemy's radar, something a F-4E can not do safely.
Also the Su-24 is the primary platform for Iran's only Anti-radiation missile, the Kh-58. While there have been reports of the missile being tested on the F-4s, the Su-24 was designed to carry it (and its successor the Kh-31) and requires no modification or special equipment to do so. Also for PGM missions the Su-24 requires no external pods to carry both Laser Guided and TV guided weapons simultaneously which the F-4 does which take up pylons that could be used to carry ordance. In other words, the Su-24 can carry a full complement of PGMs whereas the F-4 has to carry an external guidance pod.
In the anti-shipping role the Su-24 is also still quite dangerous. Its ability to hug the surface (whether it be water or land) means it can take off at a good distance away from the target, "hit the deck" under most naval radar's noses (unless they have aircraft patrolling), pop up to fire a good ranged AshM and then quicky turn away to stay out of the enemy vessel's SAMs. In my opinion airborne AshMs platforms are much more flexible in their use than shore-based or ship-based platforms.
More importantly it seems pretty clear to me the IRIAF plans to not only keep them in service but expand their overall capabilities. Why else would they modify them so they could be re-fueled by American-built tankers? Why would they be in the news for having new equipment added to them (Night vision equipment and likely GPS/GLONASS as they become available), because they know it is a fine strike aircraft and the larger the fleet the more dangerous it is.
Not only that but if and when Iran develops its own Anti-radiation missile it is the perfect platform for it.
Long story short, the Su-24 was one of the best medium to long range strike aircraft every built during the Cold War and is still a feared aircraft to this day (as evidenced by the Russians not only keeping their fleet but modernizing them as well). And considerin how 'young' their airframes are and how much they could be upgraded electronically I see no reason NOT to try and expand their fleet in the future. Simply because their use against say the USAF and USN is somewhat limited (though it used properly they still pose a big threat) is no reason to simply keep the fleet at the strength it is now. They are other possible enemies in the area and the Su-24 is capable enough to deal with them, more so with just a few upgrades.