Here's an idea I had: Give the units a scatter ability, more specifically, infantry units. This could help against units with AOE damage.
The "X" button in C&C games is used to scatter a group of selected units, to prevent AOE fire from destroying them. This could be useful against units like Siege Tanks, and timing the scatter right while also giving attack and/or move commands could distinguish better players from weaker players. I think it would have micro potential. IE: Siege Tank fires, scatter units, order them to fire while the Siege Tank is reloading, then scatter again when the tank fires. This could also allow for better Siege Tank micro-ing, rather than just deploying the unit into Siege Mode and ordering it to fire on a unit or letting it do the job by itself. This would also put less emphasis in late games on Siege Tanks for terrans, and perhaps could help units like Marines and Zerglings useful, alongside unit mixes, like Marines & Siege Tanks...

