About those power cell abilities...

No. In multiplayer they're okay-ish. But in single player power cell reloads are too unreliably few and far between.

Besides, there are better ways to have little to no cooldown (FMoA, shield usage).

Power cell abilities are basically a repository for excess skill points for me.

I'm yet to do a build where they are something I'd consider essential. I always intend to use them but never do.

Yeah same here I've not really used any of those that much I do intend to eventually on a primary build to mix things up a bit but it'll largely depend on the build it'll mostly likely be if I do a more soldier build though. But it depends on the kind of build your going for I think. I can see myself maybe using one on a secondary set of powers  on my explorer Scott but I haven't decided yet. I know my primary build will be turbocharge tactical cloak and Nova but that's all I have decided at this point.