My experience has been that drop-ins in general aren't going to give you any real gains. On almost every car I've seen, it'* the actual tubing to and from the air-filter box that are the major restriction. But the cone types do give some nice improvements.
My Duster saw about a 3hp gain going to a cone right on the throttle body, plus about a 1mpg gain as well. I had a Dreamspeed CAI on my old Avenger, and gained a real 5hp with that, but no MPG increase. My Grand Voyager gained at least 1.5MPG with a short tube and a cone, and made a noticable gain in high-RPM power.
"I have a hammer! I can put things together! I can knock things apart! I can alter my environment at will and make an incredible din all the while! Ah, it'* great to be male!"