planted tank

Anyone know?

You can get away with not vacuuming as long as you're not crazily over feeding. Heck, I prefer not to vacuum the substrate at all because it will cause massive cloudiness and possibly ammonia spike. If you're doing bare bottom like for breeder/grow-out tanks then you have to vacuum.

Water changes is dependent on your setup, specifically fertilizer dosing regime. If you're doing EI, then you have to do the weekly water change to take out the excess. If you're doing the non-co2 method proposed by tom, then you won't have to do water changes as long as you get the balance between plant needs, bioload, and fert dosing. http://www.barrreport.com/articles/433-non-co2-methods.html#post2203

I don't vacuum, it allows nutrients and carbon to buildup for the plants. Little to no water changes would help preserve those in the tank, especially with little stock. Also, don't change the filter media, just swish it in a bucket of tank water to lose the debris whenever you do a water change/filter cleaning, after a while when the debris no longer comes off, then change it. The stuff living on those is the tanks life support and you want to keep it around, the filter manufacturers just want more money.