I agree with Kirby and Michael completely.
I have made many books (with a couple of various 'self-publishing' provider such as Blurb, and Pro Photo lab such as Pikto in Toronto, Canada, and Apple). My workflow is used with Adobe Creative Suite CS5 (Design Premium CS5 and uses Design Premium versions over the years with Adobe), Apple Aperture and Adobe Ps Lightroom 3, and PhaseOne's Capture One PRO 5. My photography books included black and white, as well as color.
Before I work with my photo files for book projects, I
always calibrate monitors with X-Rite ColorMunki Photo. I recommend it highly. I calibrate my monitors EVERY week. In some instance, for extremely important project, I calibrate monitors for that project.
I notice that Kirby (or Michael) or as in many other forum discussion here at Apple Aperture community forums, I don't see any mentions of 'proper' set up with monitor in a room. For example, it is best to *AVOID ANY* light reflection toward monitor by any means. This includes reflection from bright color shirts, room wall, windows and desk lamp. Remove ALL of light reflection distractions! In order to do a proper calibration set up, you need to make sure that there are absolutely NO distractions of light reflections toward monitor. You might want to use grey shirt or black turtleneck similar to that of Steve Job's trademark black turtleneck as an example. The point is to reduce all kind of reflection of lights toward monitor. With the right set up in the 'digital workflow lab' in your room, then proceed with calibration hardware such as ColorMunki Photo from X-Rite.
Additionally, few months ago, I bought ColorChecker Passport, also a product of X-Rite. Very nice workflow, too.
Anyway, once done with proper calibration set up (and regularly), you'll do well with your workflow for your book project. But be cautious and very conservative with yourself. Don't let your eyeballs fool you. Your eyeballs aren't always accurate due to many factors involved mentioned as above. That is where calibration hardware (and specialized software that comes with calibration device provided by vendors such as X-Rite and similar high-end professional-grade third-party vendors).
Don't even think about adjusting brightness manually in monitor's physical setting, it actually ruin the entire workflow process. Don't do it! I had seen many, many, and many (if you will MANY times) discussion about it all over the Internet. This amaze me that there are millions, millions and millions of such similar problems as yours. If done manually and messing around with monitor's physical settings, this really screw this whole work up. This means bad output - simple as that. Unfortunately, some people didn't realize that. There is workaround solution to this, either use Aperture or Photoshop with level or curve adjustment.
However, like I said, once with proper set up in room setting by removing ALL kinds of distraction of light reflections, and all other proper set up (such as neutral darken shirt, wall painted in grey (specialized painting stores offer this), so on, AND IF you believe you think you are seeing some issues with certain images, use it with caution approach in Photoshop with curve or level to brighten or darken.
You want to learn a bit about soft-proofing. Aperture has this capacity to softproof your images whether your images look good for output such as book.
Understand that you can't even get 100% of what you are seeing in monitor with output (books or fine art prints etc). With proper calibration set up, this will get you very close what you are seeing in monitor vs outputs. But with extreme cautious approach, this gets very close, but not 100 percent, though. But pretty close.
You also want to learn more about ICC profile for preparing book files. I don't want to go on and bore you and afraid to confuse you even more. For example, if working with different printers such as Pro Photo lab or other self-publishing companies, or any other printers, DO consider to contact them about ICC profile where you can download these ICC profile. Please note that if they have different paper and types, consider downloading
different profiles FOR these paper used in book. But don't worry too much about this, because Apple is pretty good with books and Aperture is pretty good. BUT you gotta to calibrate monitor in order to do a successful digital photo workflow.
Well, you mentioned you don't want to invest in calibration hardware, perhaps that you want to hire a book designer to do a professional wedding book. But if you plan to make many books, DO consider to invest calibration device, this means this save you tons of time, money, effort and saving trees at the same time.
All in all, it is really up to you.
Hope some of tips, ideas and suggestion be of help and informative and educational perspective. Best of luck! Color Management topic itself is very complicated and very highly technical, it takes pro photographers, printers finally to understand what works, why and what's not. Perhaps that you want to look at X-Rite ColorMunki educational webinars about this - just to give you some ideas about why. Again, it is up to you. But the concept is the same with all other calibration device process. X-Rite has many pretty nice informative webinars. I wish that Apple offer this educational webinar about this too.
Brian