For new homes, the only question about insulating attics is how much? The Department of Energy and the 2009 International Energy Conservation Code recommend a minimum of R-38 for south central Kansas, while the Oak Ridge National Laboratory (ornl.gov) recommends R-49. We generally advise on at least the R-38 level.
For existing homes, insulating or reinsulating attics is a quick and easy process to add comfort & reduce utility bills. Whatever material may be in an attic (if any) can always be added to and, should removal be requested, we can vacuum out the existing material.
To estimate what's in your attic now, see our chart. As for what should be up there, we still recommend an R-value of R-38 in our climate zone, with higher values as an option. Whether you want fiberglass or cellulose, it's up to you as long the manufacturer's instructions are followed, you get the R-value you pay for.