The problem to is that for a country like Russia that has an enormous land mass to cover and fairly unfriendly neighbours having thousands of SA-3 systems that are medium to low altitude engagement systems remains useful... the S-300 and later systems are generations ahead in terms of performance but enemy UAVs don't require S-300 level performance... when jamming is heavy a few home on jam or optically guided previous generation SAMs can be rather useful.
Their main problem was lack of mobility and the size of the electronics and support equipment made most of them relatively fixed systems though there are modern upgraded electronics systems for them that can allow them to operate from the back of a truck if needed.
The old SAMs are relatively fixed systems, but then a capital city or an airfield is also pretty fixed too.
With a modern IADS and modern mobile missile systems the older systems can offer cheap support... remember an aircraft turning hard to evade an SA-2 might need to dump ordinance to do so and that manouver could bleed speed or altitude or both making the aircraft more vulnerable to any other missile launched at it.
In some backwater places where there is nothing worth protecting moving a few old SA-3 batteries makes more sense than building S-400s, but as the old missiles expire and are used for target practise or in exercises then Vityaz will likely replace them giving a huge step up in terms of performance regarding range, number of targets engaged, type of targets that can be engaged etc.
If the requirement is the ability to bring down a hijacked airliner that is going to be used as a missile then something like SA-3, SA-2, SA-5 would all be very capable systems... and with upgrades even more so... but the original systems were very expensive, and maintainence costs while reduced with upgrades could be an issue... though it will still be cheaper than buying all new state of the art systems.
The sheer size of the old missiles would allow plenty of space for more modern seekers including ARH and or IIR, while improved control surfaces and increased thrust rocket motors could create far more capable missiles... most of the huge boxes of electronics in the ground control systems could probably be replaced with a modern laptop...
The thing is that you have to be careful you don't end up changing everything and ending up making a mistake... remember that hammer you had that was the best one you ever bought... it lasted 30 years and only had 3 new heads and 2 new handles....
Looking at putting in new Seekers and new fuel and control surfaces and new launch equipment... it might make more sense to just buy older model S-300s, or even look at Vityaz lite.