Trent Roman wrote:
Unless one can devise a way to keep shields up and fire weapons while cloaked, I don't see the cloak as being particularly useful in combat--not at the speed at which weapons exchange takes place. It's use would be primarily one of mobility: getting your ships to location XY undetected, concealing your ship movements from the enemy, etc; all of which falls apart as soon as the enemy finds a new way to detect cloaked vessels.
Fictitiously yours, Trent Roman
About detecting cloaked ships - the Federation had problems detecting klingon/romulan cloaked vessels for centuries - and it still has. It's a cat and mouse game - you build a better trap, the other side builds a better mouse.
But a cloak doesn't have to be perfect to be efficient.
Nowadays, stealth tech is far from perfect; and yet, it gives its possesor a significant advantage. That's why USA and other countries spend billions on developing such technologies - an enemy that can't see you reliably until it's too late is a defeated enemy.
As for the edge a star trek cloak can give you:
You can hide the position of your fleet from your enemy at all times - which gives you a gigantic strategical advantage;
As you said, you can assemble a large invasion fleet and mantain the element of surprise until you fire the first shots - too late for an unprepared enemy;
You can also attack key bases deep in enemy territory with only small forces;
Cloak even gives you an edge in ship to ship combat: The "vulnerability window" between full cloak and full shiels is only a few seconds - with inspired piloting, the chances of you being hit by a surprised opponent are minimal - on the other hand, you are prepared, your weapons target a critical area of the enemy ship, enabling you to deliver a devastating first strike. In "Star Trek 3" and "DS9:The die is cast", this is exactly what happened.
Even more, apparently the latest generation of cloaks allows you to fire - and activate shields - while your ship is hidden - I'm referring to "Nemesis";
When your ship is damaged or inferior to your opponent's vesel - when your fleet is outnumbered - you can engage cloak and escape death or defeat;
And then there are the obvious intelligence gathering possibilities.