From what I've heard, and through personal experience with my previous set of speakers, the carpet spikes will improve your speaker's low end. They "couple" your speakers to the floor, which can help tighten up the bass by giving your speakers a solid foundation.
To make an exaggerated example of NOT using carpet spikes, pretend you put your M60s on a bunch of ball bearings. With every movement of the speakers cones, there's an equal and opposite movement of the speaker cabinet. This would result in your speakers wanting to move backward when the cones are movign forward, and vice versa. The end result is muddier sound.
Granted, your carpet is probably not frictionless, but I'm sure there is some give to it. I'd definitely recommend using the spikes. As long as you don't forget they're on there and start dragging your speakers across the carpet, they won't cause any damage.
Enjoy your new system!
