Sticking to the core mission vs making the most of opportunities

I read an article today about Apple's patent for a smart bike, making me think about whether this is something that it's in Apple's shareholders' best interests for it to be doing. Here are some arguments for and against companies expanding out of their normal area of expertise:

Arguments for

• If an employee has come up with an innovative idea, it will be motiviating to that employee and other employees for the organisation to pursue it (it will also make the company a more attractive place to work, helping recruitment and retention)
• Potential for more revenue
• Potential to diversify the revenue base, making the company more stable and therefore more valuable
• Potential to increase brand value by reinforcement (i.e. making the brand more common), and by associating it with new and innovative products

Arguements against

• There is potential for the failure of the venture to cost the company money
• There is potential for failure of the venture to cause brand damage, or that even a successful product could dilute brand value due to differences to the core product line
• The lack of expertise in a new field increases the risk of failure
• There is the potential that the venture could distract management time away from more important issues