What to do with those other ideas

I just saw a new comment added to an old post on what to do with an idea - its a question actually, and answering it seems like the thing to do.

The original post was about answering a question from a fellow traveler and walked through the 'doing the due diligence' and vetting the idea before building anything. But this question, from Anonymous, is 'what if the idea is not for a product, but for marketing or advertising?'. Anonymous doesn't give any any more background info, so I get to have some fun hypothesizing (and take a break from spread-sheeting).

So, where's Anonymous coming from? I'm guessing s/he is not currently in a position of power and influence which would make this question unnecessary - probably just one of the rest of us. But what Anonymous is currently doing and wants to do also have an impact on how this question is approached.

• Works in an established company and has an idea for marketing/advertising a current or upcoming product. Anonymous must do what any 'intra-preneur' would do: build the business case and build contacts who can champion the cause with the ones with power and influence ('investors").
• Works in a startup. Ditto, except it'll be at 3X speed, and you shouldn't have to build contacts in the startup (if you aren't drinking buddies, you should at least be watercooler ones) and you may beef up your story if you have some outside experts weighing in. Key point, do the homework and build the case - and you'd better be really motivated, as you're probably putting in crazy hours already.
  
• Works/studies somewhere else and has a great new idea for marketing/advertising and wants to start a company with that. Same process. Though this is a service, not a product, it is still something to sell to customers (whoever they may be), so Anonymous has to go through the same steps of scoping the market, value proposition, pricing etc. and maybe pilot (aka give it away for free) with a couple of customers before deciding this is a keeper.

There is an undeniable pattern here. Regardless of what the idea is about, and size/stage of the company involved, the first thing to do is build a business case. To sum it up (in an advertising homage): do the due!