A fair bit?
He wrote
everything with Noddy Holder and Noddy's contribution became less and less over time, by the last few albums, Slade had become the Jim Lea band.
All the clever pop harmonies, the hymnic chorusses, that is Jim, just listen to his comparatively recent solo album which sounds like Slade without Noddy singing/screaming his balls of.
As regards his bass playing: Of course he was technically proficient too, but what made him outstanding as a bass player was his sense of melody - McCartney-esque -,
http://www.youtube.com/watch?v=Gnf-RjWRlXs&feature=related (that's him on the violin too, that is where the melodic influence comes from, when he joined Slade he didn't even play bass)
not lightning fast 12 bar runs. Actually, the US is once again to blame for that too: He acquired that style of playing during Slade's "forgotten years" as an opening act in the US when his combined violin/bass solo (often from atop the PA cabs) was supposed to catch attention for Slade while people were waiting for whoever was headliner. Nothing impresses Americans more than athletic skill.
