The 25-year-old Spruce joined the Bulls yesterday for a fee of pounds 120,000 and will go straight into the side for the match against Leeds at Odsal tomorrow night.
Smith has been tracking the player ever since taking up his post at Bradford.
"I have kept in touch with his development since he was a young player in the very good Widnes sides when I was coaching at Hull," he said. "He is one of those players who, if he works hard, could develop into one of the best in the competition."
Smith said that the signing of Spruce brought his current spending plans to an end. He now has enviable depth among the backs, with both Paul Cook and Nathan Graham able to play elsewhere, and anything less than a top four finish in Super League would be considered a disappointment.
Widnes have pledged to use the money received for Spruce to strengthen their own First Division promotion push.
Smith's younger brother, Tony, has been appointed assistant coach to Ross O'Reilly at Workington. The former St George player joined the club as a player earlier this month, but broke a bone in his hand in his second game.
Wigan confirmed that Craig Murdock will play scrum-half in the return match with Bath under rugby union rules at Twickenham on Saturday. The regular scrum-half and captain, Shaun Edwards, has ruled himself out with rib ligament damage.
The sport went back to court today in Australia with the opening of Super League's appeal against the ruling banning it from kicking off there before the year 2000. Seven days have been set aside for the hearing, in the federal court in Sydney, with Super League's lawyers arguing 62 points of law from the original marathon court case.
If Rupert Murdoch's organisation loses again, his only remaining option would be to seek a hearing before Australia's high court, although speculation is strong that he would instead cut his losses and concentrate on his rugby union investments.Reuse content