If your HDL levels don't move, ask your doctor about stopping the Niacin and putting you on VYTORIN. Its a statin with the addition of Zetia, which is specifically targeted at improving good cholesterol levels.
Where do you currently sit for your overall Cholesterol, your LDL and HDL?? If the niacin has your LDL and your overall at good numbers I'd be content to leave well enough alone for the time being. If, however, you still aren't reaching the numbers you want on the LDL and overall cholesterol, you might want to give up the niacin and look at a statin like Lipitor or Vytorin. Even my Endo who is in his mid 30s and looks like he's in great shape takes Lipitor "just because"! He says in his case, its better to be safe than sorry!
Soooooo.... don't let your numbers go out of the zone for more than 3 or 4 months ( a good time period to evaluate the efficacy of your dosage and approach) before you change up your approach to pull them back to where they belong. BTW...Lipitor is one of the most studied drugs out there, next to asprin, and it has a great safety profile!