I think you'll find this was a 50-50 decision on most owner's cars. I went without my foam- it just felt like the MSD seated better without it and I wasn't concerned about any mechanical noise suppression. It's been on the car for 4yrs. now. I've re-torqued the bolts once. All is well.
If anything, it allowed for a channel of cooler air to pass under the IM in my mind. Folks have used the opportunity to apply stick-on heat shielding to the bottom of the IM at this time. But people have done it both ways without adverse effect I believe.
I should add that you should follow the install directions implicitly- no dork wrench, invest in a good INCH/lb torque wrench and make at least 3 passes with blue loktite, etc... as instructed.