BC was released nearly seven years ago. That's like 10 or 11 generations in computer terms. So if you're still running on the same hardware you had then, maybe it's time to upgrade.
If your hardware still meets WoW's recommended capabilities, then hardware should not be the issue. In that case, I don't know what to tell you. nUI should not be killing your online experience if your hardware is adequate.
Before I switched to nUI, I used IceHUD. Not sure, but I think it's still around.