Should I agree to have more insulation added to my attic?
Good question.  First off, there is no "code" requirement that would mandate adding insulation to a 6 year old house. The current standard in new construction is to try to achieve a R-42 in attic spaces. Adding more insulation to your R30 is not a bad idea, however I have a few questions for you. What kind of insulation do you currently have installed there now? What are the dimensions of the space and style of house and source of heat and A/C. 

Adding more insulation is almost always a good long term investment, but before I would trust a sales pitch from a door to door vendor, I would investigate alternate routes. If a DIY project, costs to simply add a layer of R 13 or R19/23 fiber glass blanket over my existing insulation.(assuming it is also F/G blanket style). I would also seek quotes from a couple of reputable energy conservation/insulation contractors in your area. A good contractor will ask you the same questions I have, and ask about your energy costs now, then calculate the potential energy reductions in hard numbers or percentages and expected pay back period. Some energy audits are offered at a reasonable fee or even free and address several aspects of comprehensive energy savings in the home. It can be amazing what a little caulking, joist/wrap box insulation, weather stripping, hot water conservation methods and increased attic insulation can make in your total energy picture. Does your state require a professional license or certification for this kind of work? Be cautious and seek a trusted professional opinion.