The midfielder struck in each half, either side of Nicky Maynard's ninth of the season for the Railwaymen to make it four matches unbeaten for the Hatters.
Luton took just five minutes to open the scoring after a horrible mix-up in the Crewe defence.
There seemed little danger as debutant Ed Asafu-Adjaye lofted a long ball behind the visiting defence, but as goalkeeper Ben Williams advanced from his line, Danny Woodards cleared straight into the path of Spring who fired into the empty net from 30-yards.
Crewe briefly rallied as Joe Anyinsah's run set up fellow loan man Steve Jones for an 18-yard shot that was blocked by Don Hutchison.
After that it was all Luton as Paul McVeigh saw a 20-yard shot deflected over in the 19th minute.
Stephen O'Leary fired wide from the edge of the area six minutes later and McVeigh then flashed an angled drive just past the far post after a neat one-two with Ryan Charles in the 36th minute.
Charles then scuffed an opening wide from 15-yards in the 39th minute, before the half ended with two scorching long-range drives from Spring - the first pushed aside by Williams and the second arrowing just wide.
The Railwaymen finally registered their first shot on target 40 seconds after the interval when Maynard exchanged passes with Anyinsah, raced into the left-hand side of the area and fired straight at Dean Brill from 12 yards.
O'Leary tested Williams with a 25-yard snap-shot in the 58th minute for the hosts.
But just a matter of seconds later the Alex were level when Kenny Lunt dissected the defence with a neat through ball and Maynard nipped in behind Keith Keane to slip the ball under the advancing Brill for his ninth of the season.
Luton responded as O'Leary played in substitute Calvin Andrew, whose15-yard effort was pushed aside by Brill.
From the resulting corner, Patrick Boyle took down Charles in the area and Spring converted the 77th minute penalty to seal the points.