Of course the saucer section was instrumental in the capture of Locutus and thus the ending of the borg threat. Had Riker left it behind Earth (and the saucer section) would have been assimilated.
There were plenty of saucers at Wolf 359. A lot of good they did.
Actually it was the shuttlecraft that was the more the key. The saucer was just a diversion.
More precisely, it was the extraction of a single particular drone that proved essential, as it turned out that the whole Cube had a critical weakness that could be exploited through Locutus. Riker didn't even know that at the time; he just wanted to rescue Picard. Even Shelby hadn't figured out that rescuing Picard might lead to the Cube's defeat. With all their saucers, shuttlecraft, and stardrive sections, it's really doubtful that Hanson, or anyone else in his fleet, figured it out either. They had a different priority than rescuing a single officer: stopping the Cube.
However, if Hanson had figured it out in time, he still would have had plenty of ships, saucers, and other sections to make whatever diversions they would need to get something inside the Borg's electromagnetic field to transport a landing party -- sorry, away team -- to and from the Cube. We know that, because Riker did all that with a single ship.
Strategy, not saucers, was the key.