You may well be right, I’m basically just echoing what I’ve read. But I’ve never read that the Germans actually wanted Norway; my sources all say they just didn’t want the Brits to have it.
That's what I've always heard as well.
It's a matter of interpretation -- your sources are not wrong, in this sence: in December 1939, Hitler told his Admiral Raeder and Norwegian Vidkun Quisling that Germany would not invade Norway as long as Britain respected Norway's neutrality.
However:
"In October 1939, the chief of the German Kriegsmarine, Grand Admiral Erich Raeder, discussed with Adolf Hitler the danger posed by the risk of having potential British bases in Norway and the possibility of Germany seizing these bases before the United Kingdom could."The navy argued that possession of Norway would allow control of the nearby seas and serve as a staging base for future submarine operations against the UK"
"...Convinced of the threat posed by the Allies to the iron ore supply, Hitler ordered the German high command (OKW) to begin preliminary planning for an invasion of Norway on 14 December 1939. The preliminary plan was named Studie Nord and only called for one army division.
"Between 14 January and 19, the Kriegsmarine developed an expanded version of this plan."
All of this is considered "low level planning" and it did not become "urgent" until the Altmark incident in mid-February convinced Hitler the Brits would not leave Norway untouched.
My argument is, the Altmark incident was not the "reason" but only the pretext for Hitler's reaction.
The real strategic reasons were those expressed by Raeder back in October 1939.
Indeed, the Brits also had plans, especially to help the Finns, but when the Russo Finish war ended on March 13, the Chamberlain government was not willing to consider invading Norway against its will.
By the end of March that changed, and the Brits also cobbled together a Norway operation. But the Germans were already far ahead, and after months of methodical planning, outmaneuvered and defeated the last-minute British effort.