On the subject of units and maxing them out, a little rant. Keep in mind, this is based merely on watching over the shoulders of people who follow Starcraft matches.
Starcraft, being an RTS, allows a bit more interaction between units than a TBS a-la what we have here. The basic concept is Damage-Per-Second, its meaning obvious. However, many (all?) of the high DpS units are also very low on hitpoints. Add to this the existence of splash damage and you have an interesting situation.
If you want to maximize the damage you could inflict (in theory), you'd build Marines*. However, though your Marines would outdamage anything that only equals their cost, you would not attack units that can either outrange them or kill them with a wide damage area. You would not use Marines to attack Tanks (high range, splash damage), Lurkers (hidden, insane area of damage) or Templars (large damage area for a certain ability).
already the analysis gets complex, as I think the unit with highest DpS is the Zergling with attack speed upgrade. However the Zergling is Melee, while the Marine has range and can start concentrating a lot more firepower on something, and a lot sooner.
A similar mechanic in a TBS like TBfGB, which allows fully custom units (and I love this feature of it) may need the costs to be a bit wonky (quadratic? mixed formula on different attributes? but not exponential
that's just cruel).
Another TBS system I looooooove
is the Disciples one, not least because it involves very few units per battle and is usually very fast to resolve a battle**.
Apart from special boss battles and sieges, or the occasional time when you purposefully attack a strong opponent with weak but very buffed up units to level them, most battles get decided in two-three turns per side in my experience.
A "stack" is actually a group of at most 6 units, one of which is a commander. All units gain experience from winning battles and all may level up, from knaves with a pig sticker into awesome warriors to challenge Hell. There is no movement in combat, the stacks simply stand in front of each other in 3 rows of two columns. Usually front is occupied by tough units to protect the back, where more fragile (and more damage-powerful) units are placed.
It has its warts. Magic is so ludicrously powerful for beefig/nerfing units that being out of turn in the open is painting a bullseye on your head.
The whole point of this is lost if you keep it a secret.