Dude, the rhythm section is a vital ingredient of Maiden's sound, more than any other band. Not that other drummers can't do it, but I wouldn't think to lightly about it.
Clive was very good as well, but a very different drummer. Better than Nicko when it comes to most of the songs from his era, but I wouldn't be so sure if he can do (when healthy) all the stuff Nicko has done. I remember an interview with Harris, in which he said that with the arrival of Nicko, Maiden's songwriting has changed/broadened.