I agree with manaical that I'd find them interesting if they were functional and not aesthetic.
The simplest formation might be to go to Napoleon times and have a column vs. line formation in which units in column travel faster but take more enemy damage, or what not. Or you could make formations kind of a hot-key micromanaging ability like say Rome Total War does.
It sounds like you want to simulate military formations down to the individual soldier to simulate the dynamic value of formation. In which case you probably want to get a look at the tactical reasons for formations. And that varies with time period. For instance classical eras would have overlapping shields which is the main value of formations at all, besides being able to quickly bring up reserve forces to a melee (I recall Romans had staggered spaces between each Century (not Centurion) so a fresh Century could come up alongside to support a Century already in melee.
Formation tactics in the age of pike and gunpowder were quite different, but basically allowed for complementation of unit types. That is pretty much what the Shogun 2 Total War formations get at to (complementing pike, melee, cavalry and missile).
Tactical formations (dismounted) in the era of assault rifle and machine gun infantry are all about making contact with the enemy with minimal risk, and then responding with maximum firepower frontage. To some extent it's about fields of fire too for the supporting weapons and to minimize friendly fire incidents. But it's a lot like Napoleon times (some formations for speed, some formations for maximum "frontage"), just with more dispersive formations.
I think what you're trying to do is really not how most RTS games approach unit combat.