I haven't found elastacross string savers to promote main string sliding and snapback. I've used them in a pattern in the center of the stringbed and my perception is that they a) separate the strings enough to increase the angle of the weave, which effectively increases the forces pushing the strings together, and b) constrain the strings so that they must move more linearly along the crosses than they otherwise would. Together, these two effects reduce the distance the main strings slide sideways and effectively increase string-on-string friction, which would reduce the speed at which they snapback. But they do reduce wear at the intersections and after hours of play they should allow the stringbed to function pretty much as it did when the stringsavers were first installed. So taken together, I think a pattern of stringsavers constrains and reduces the efficiency of the snapback mechanism but also allows the mechanism to continue to operate at that reduced level of efficiency for a longer period of time.
A better stringsaver would be flat and very thin, so that it wouldn't increase the angle of the weave and wouldn't constrain the strings and force them to move along the "track" of the stringsaver. This guy's aluminum string savers are almost ideal: http://tt.tennis-warehouse.com/showthread.php?t=246634
Even better would be if you could attach small, thin, flat sheets of teflon at each intersection. If this could be done you could use natural gut mains and crosses and get poly-like main string snap back that would not diminish as the strings aged.