[Cloaks]'ve always been shown to be power-intensive devices
Have they?
The prototype Romulan cloakship was running low on fuel at one point of her mission, but that's about it. The devices we see (or don't see) are portable and can apparently be hooked to any sort of power socket ("
Enterprise Incident", "Profit and Loss", "Emperor's New Cloak"); in absence of one, they can cloak themselves on internal power only ("Emperor's New Cloak"). The cloak installed on the
Defiant was never said to be a major power drain, nor did the Klingons or Romulans complain of such things after that single "Balance of Terror" incident.
The idea of designing ships to be compatible with cloaks is a sound one, though. One does have to choose the kind of desing where assorted emissions are either minimized or then concentrated for easy concealment. Klingons might have designed their 23rd century BoPs with cloaking as a primary criterion; they might also have designed their cruisers with such things in mind, although ENT "Unexpected" suggests that Klingons didn't have cloaking before they designed their main cruiser lineages. Probably cloaks are still worth the while on unoptimal ships, but serious cloak-and-dagger work is best carried out with custom designs - hence Kirk and pals jumping to the conclusion of "Klingon Bird of Prey!" in both ST3 and ST6, despite the very real possibility of other Klingon ship types being capable of cloaking as well.
The Borg do not believe much in customizing, that much is certain. Their hyper-generic designs might indeed be a hindrance in achieving optimal invisibility. Then again, they
are a secretive bunch... So perhaps low emissions, low sensor albedo and other stuff of that nature are chief criteria in the construction of Borg vessels already, and visual invisibility is just a meaningless optional extra that doesn't hold much attraction to the Collective?
Timo Saloniemi