Your representation by a Realtor will include marketing, industry knowledge (the ins and outs of the process, title, inspections, etc.), local market knowledge (your competition and trends), probem solving abilities, contacts, negotiation skills, presentation skills, organization and follow through.
Yes, marketing is a very important component. But, really, what you are paying for is the package bundled together that make a great Realtor.
As far as marketing, are you talking about print or online. By far, buyers are on the internet in search of property. Unless you are deeply in tune to the industry, it will be easy for you to miss some of the best opportunities. If you request your Realtor to review all these potential opptys with you, the time investment for both of you may supercede that which is productive for either. Many agents have broker support that helps them with many online placements. Your agent will not be able to restructure the broker portion of the commission split, since it is under a contractual arrangement. For example, our company feeds all listings to Trulia for all of our agents. This is an automated process managed internally by staff. It would be more costly and time consuming for us to pull your lisitng from data feeds than it is to include it. And, Trulia, for example would not be availabe for you to upload directly.
I understand that your intentions are good. You want to play an active role and you have confidence in your own ability to build marketing materials. I don't doubt that you might be talented in that arena. Perhpas you could draft some descriptions for your propery that might help in the copy writing. A side note here is that I have seen several violations of fair housing laws in brohcures made by FSBOs. By working with your Realtor, you skills in graphics, marketing, or copy writing might make for a winning team.
If you were considering investing in print ads and paying these out of pocket in lieu of a reduced fee with the Broker, I would advise you to save your money on the print ads.
With absolutely not an ounce of disrespect intended, the help that you could lend on marketing represents only a minor part of the total marekting. For example, networking with other brokers is a value that cannot be replicated. The websites that must be accessed by Realtors, the review for compliance w/ fair housing.
You can certainly discuss w/ propsective Reatlors their willingness to offer any discount for your contributions to the marketing efforts. Don't be offended if the discount is somewhat minor. There is so much that a Realtor does that goes on behind the scenes. It is reasonable that you would not be aware of this.
Perhaps a Realtor might grant you a disocunt. In closing, don't pass on a great Realtor if that person is really the best for the job. Look at the big picture and what you stand to gain or lose.
Best of luck!