“If someone sold in 2005 for a great profit (say 300k) after 2+ years of ownership, are there any tax issues with waiting? In other words, would they need to buy again in a certain amount of time to avoid the 15% + 9% state tax on the profit?”

If you are a married couple and this was your primary residence you would not have to pay any taxes. If you are a single person, the first 250K profit would not be taxed, but the 50K would.