I see no reason why USC's spending would slow down anytime soon as they've already gotten an immediate return on investment. Riley inherited a 4-win team and turned it into a 10-win team with a Heisman-winning QB who followed the coach who recruited him out of HS to his new job.
They just landed the 7th-ranked recruiting class with headliners at QB/WR and now they're fortifying their trenches via the portal. Premier QB's and WR's have been and will continue to flock to play in Riley's offense.
Their schedule sets them up very nicely as well to have at least another 10-win season. If Williams stays healthy, there's no reason why they shouldn't earn a playoff berth and continue reviving their once-dormant program.