What the hell, it's the weekend...
Here's a third option:
Five men work at identical jobs on a shop floor. Four of the men attest to the work's absolute drudgery. They have trouble getting to work on time in the morning, find every excuse to take a break or leave early, and dream of the weekend. The fifth man is absorbed by the work, is constantly getting better at it, and leaves at the end of the day happy, with a feeling of accomplishment. This scene is repeated in many different fields of work, all across the world.
When the work to be done is the same, how can some people find it drudgery and others find it fulfilling? Obviously, the difference is not in the work, but in the head of the person doing the work. Which leads to the conclusion that, if you can change your mind, you may be able to make the uninteresting topic as fun and fulfilling as the one you currently enjoy.
This change is not a matter of willpower, but a matter of how you view the work, how you structure the work, and how you direct your attention. If you reflect in detail on how it is that writing about the "fun" topic is enjoyable, you may see opportunities to make the topic of your choice enjoyable.
There are three principle obstacles to making a task an enjoyable one: too little challenge, too much challenge, and poor feedback.
Too Much Challenge
Writing about a different topic could be unpleasant because it's unfamiliar, and it's more enjoyable to stick to an area where you already have considerable expertise. One approach to simply be aware of that problem and structure your work as a learning project. For example, when you are learning a new topic, you are in a unique position that experts in the field have lost -- you understand exactly what things newcomers are likely to find confusing and misleading. You're in a great position to write tutorials and introductions and "how I learned about X" pieces.
In effect, for any unfamilar topic area, you are already an expert at one aspect of that topic: the problem of learning that topic. This can help reduce the challenge of tackling new subjects to enjoyable levels.
Too Little Challenge
Writing about a different topic could be unpleasant because it is too simple, involves no learning at all, is fairly mechanical writing, etc. In this case, it is possible to introduce challenge by redirecting your attention to other nuances of the work to be performed. For example, you may be able to structure the boring material in a unique way, or spend more time devising graphical aids. Or, you might focus on devising techniques for completing the work more quickly, or focus on how the writing can better support the overall SEO.
Is the topic boring? Then why are people searching for it? Do your writing with an internal focus on discovering why some people find it interesting. Subscribe to the Wall Street Journal for a while and you'll see that they write about all manner of obscure human activities -- and they find what's interesting about them. A basic curiosity about other human beings can translate into an interest in the wide variety of things that they inexplicably are drawn to.
Highly enjoyable tasks always involve some kind of feedback, information that tells you how you're doing, so you know how to change your performance for the better.
One reason people become "hooked" on the SEO game is that they have systems that give them detailed feedback on how they're doing. They make changes, then they watch a complex picture of how their changes affected their SERPs, perhaps even for hundreds of keywords. There are opportunities to make this game endlessly detailed and nuanced, especially since a key player in the game, Google, is always changing the game.
But it is also possible to construct feedback systems designed to make the writing of content equally absorbing. Picking a few keywords and writing some articles about them is a common approach, but much more is possible. For example, you can take boring topic A and map out an initial universe of a couple of hundred search terms, and begin defining work items for each of these terms (e.g., creation of new pages, enhancement of existing pages). Instead of "I have to write about X", turn it into the construction of detailed strategy and tactics for building content that takes over the complex keyword space (much of it lying undiscovered, initially) that topic X represents.
If you believe that Google penalizes a sudden burst of content in one keyword area, you can have your system parcel out these work items such that work progresses incrementally across a variety of URLs and keyword areas (even though the research of what to do was quite "bursty" in particular areas). Dividing the work to be done in different ways can have large effects on its enjoyability (e.g., "mornings I do research and define work items, afternoons I build content to check off work items, and the last half-hour of the day is studying traffic trends.").
You can make a system that lets you quickly see, for a given URL, all the Google search terms that have hit that URL in its lifetime. This can generate a need for new content, a need to tweak the existing content of that URL, etc. You can make a system that shows you how your "volume" of work relates to the "volume" of traffic that results, and what the lag between the two is (and what keyword areas have the best payoff in this regard -- and anything else you can think of that interests you :-).
You can make a system that records time spent building particular content and (for example) tries to measure AdSense income for that content and relate the two. Is it worth making a page for that 4-word search term that probably will only provide a couple hits per day? Let's look at how some other perhaps similar terms are paying off. Etc.
Your system can let you see, for a given search term, all the Google queries that contained that search term, and all the URLs that those queries hit. Your system can show you how this day's/week's/month's traffic for a given search term or URL compared to the previous day/week/month (and indicate whether that change was statistically significant). Your system can show you whether any given new/changed URL was indexed by Googlebot since your last change or not, and what the typical lag is).
The ability to surf your website's keyword/traffic space in a variety of ways can make constructing even the most boring content interesting -- it becomes a means to a more interesting end. There are as many opportunities for feedback systems (with colors, and charts, and graphs, etc.) for content construction as there are for SEO; indeed, they are highly related activities.
The point is not that you need the most complex support system in the world, but that if you find ways to construct feedback systems for your writing, you'll likely find the task of writing more enjoyable, even for areas that are not implicitly interesting to you.
The starting point is simply realizing that what defines "play" versus "work" is almost completely in your head, and is under your control should you choose to exercise it.