You mentioned Helpless, so I'll start with the idea that she lost her powers. In that case, I think she'd be pretty miserable. Knowing what she knows, and how she used to have the power to do something about it, would be torture. I wonder though, if it'd be the same for her if her powers were somehow taken away from her in season 6? For example, (and I actually thought this was going to happen when I first watched it), if she'd come back without them. Maybe she would have felt such incredible relief. Yes, she was back and things were terrible in many ways, but it was no longer up to her to make it right. To make the gut-wrenching decisions. But I think that by season 7 or so, she'd feel differently; she'd go right back to missing her powers.
If she'd never had any powers to begin with? As others have said, I think that depends on how much she knew about vampires, demons, etc. Knowing all of that exists but not being able to do anything about it would be pretty downright depressing, I think. But if she were completely oblivious? Who knows? She'd probably have stayed in LA, graduated with mediocre grades and a boyfriend who'd encouraged her to stay local for college, but ended up leaving her for someone else during freshman year. Because Buffy is naturally smart and resourceful, (or are those qualities just the result of the slayer power? I'm going to guess not for argument's sake), she would eventually figure things out and be just fine. I mean, who knows?
Of course, given all of the nasties that Angel and co were busy fighting in LA, she'd be in danger quite often, (as are all residents of LA and Sunnydale, apparently). So there's that thought...