Selling Articles and Photos
Let's break things down into two areas: payment and rights. Obviously, you want to maximize the pay you get. Remember that the photo department and its budget are usually separate from editorial. It always makes sense, then, to ask the photo department what it would normally pay for images.
Sometime publications will pay a daily rate plus expenses. Some pay by the image. Some have a flat fee in mind for a certain number of images. Generally, the amount is going to be significant in comparison to the writing. I've personally had assignments where the photos paid about as much as the writing did. In the worst case that I can remember, it was still about a third of the fee. There are cases where the photography could run more than the writing.
Only after you've understood the publisher's photo pricing can you know if a bundled price give you more money or less. The publication wants to minimize the total, because then it saves money is is more profitable. You can also reasonably guess that the publication is unlikely to pay you more in total than it might otherwise. Unless you have a sense of how the photo department pays, you won't know if you're maximizing your income. I wouldn't give a break in pricing for getting both parts of the business. By having only one person go to an event, the publisher is already saving on expenses. You want that to be the source of cost reduction.
When you bundle two services together in pricing without explicit acknowledgement of each contribution, you effectively devalue both. If the publication decides to use some extra photos, well, it's already paid for them in the word rate and doesn't need to pay the addition that it might. You've eliminated an argument for getting a future rate increase because the editor thinks that should include something additional - more photography. But for all you know, some writers might already get a higher per word fee than you.
Now lets discuss the rights portion. When you bundle things together, you also start lumping together rights. But photographers generally give less generous rights packages. Why should you be unable to sell the photos for six months? Because you think the publisher should have that long with the story? The idea of exclusive use for a period of time is usually to keep something away from competitors. But if you treat photography separately from writing, you can possibly get more nuance in negotiations. For example, if you sell directly from a web site to people who might like an image, that shouldn't be competitive, and so, shouldn't be part of an exclusive run. (I'd actually think six months was too long even for writing. Try three, or even two.)
In summary, by bundling, you impair your ability to get better terms on rights, and you potentially devalue your work. I think separate pricing and rights negotiations are usually the better choice to sell both writing and photography.
As for publishers who expect writers to provide photos for a single fee, consider what you're actually doing. Say that the photography would typically run half of the writing fee (and, again, that's not wildly optimistic). So you're selling 1.5X, where X is the writing fee. Now divide the package price the publisher offers by 1.5. If the amount is, say, $1,200, then your writing is actually bringing only $800. If someone offers $600, then the writing is only bringing $400. Ask yourself if the amount you get seems reasonable for the writing alone. If not, then pass on the project.