I don't think a little bit of ich necessarily indicates a need to treat a DT or set up a whole tank QT if the fish are otherwise healthy and eating well. A bit of ich is often, however, an indication of stress, especially if you QT'd your fish and there were no recent additions. Once the stress is resolved, the ich will usually go away, if fish are healthy. I consider something like this a warning that the tank environment needs attention. Could be:
water changes/water quality improvement
diet needs to be diversified/improved
aggression/territoriality among fish
stress due to lack of hides (even if fish are not fighting)
stress from too much noise/activity in tank room
etc.
Some people have mentioned they think you may need more hiding spots for fish that can be territorial and like to have caves. I wouldn't take the aquascaping suggestions to be anything but ways you might consider to reduce the ich. The idea that stress is behind it is valid.
I've had ich show up in my long term established tanks periodically. Thankfully, not too often. There has always been a reason for it, that once resolved, resulted in the tank being healthy again.
Most of the people posting are honestly trying to give you good advice. Whatever you do with your tank is up to you, but don't take sthe advice personally if you disagree.