I don't have a Tax Loss to harvest, but have some gains.
Is it advisable to sell my gains and re-buy the fund so that my gains are taxed at a lower rate?
If you are paying 0% tax this year on the gains, the answer may be yes. Or if you are likely to sell within the next year, it may be yes. Don't forget to include state income taxes if any.
Everyone's situation is unique - for me, there seems no reason to gain harvest. In California I'd owe 15% to the Feds plus upwards of 10% to the state. Taking that hit in 2012 means my investment would drop by 1/4, and even though this is less than the hit next year, it implies a loss of the compounding benefits of deferring the tax to some indefinite far future point. That lost compounding benefit is significant for any time frame longer than a couple of years. The net change is 5%, plus 3.8% if you're subject to the new Medicare surtax. Against that are the likelihood of avoiding the surtax entirely on lower retirement income and/or the possibility of living in a state with a lower tax rate in retirement. Given this, I have gain harvested only positions that I was likely to sell within a few years anyway, in my case concentrated positions I don't plan to hold until I retire.