To make any money, you need either:
1. A big hit.
2. Medium success writing series
3. LOTS of shorts
That's pretty much the entirety of being an author. If you're a one trick pony, it better be damned good. If you're not, being prolific is the way to go.
But writing in multiple genres, possibly under multiple pen names, means a less 'rollercoaster' experience. When vampire novels wane, they drop off completely. Novels are subject to a certian fad element where one big thing jumps off the shelves for a year or two.
One way to combat that is to write widely. I still think cross pollination is a bit of a myth, and that narrow branding is better for most authors. Readers like their crime novels to be crime novels, and if you write 1 crime then 1 romance then 2 sci fi... it gets confusing. Similarly, don't start dozens of series and finish little/ none of 'em. It's plain unprofessional.
So a balanced portfolio probably involves writing multiple series under multiple pen names, and hoping one strikes it big... while still planning well enough to make a living wage if you end up firmly in the midlist. Not an easy task.
Dan and I have a little spread. Our major work, under our joint real names, is crime fiction. We love it. But, crime is a crowded marketplace and it can be very volatile. It's easy to go from 500 sales a day down to 0 then back up again. Just having crime novels could be quite unpredictable. Baked beans on toast one month, champagne and caviar the next. Sure, more titles means less volatility... but these novels take a while to write. Crime means planning. Readers are uber picky on procedure, forensics etc. I still get emails complimenting us on blood spatter accuracy, and likewise get emails accosting me about the rarity of taipan neurotoxins. I'll admit to taking a little creative licence on the latter - it's a fun story.
But we also have psuedonymous work up - and that helps with income levels. I've got non-fiction legal titles up. Not huge sellers, but enough to justify hitting publish.
Dan's hoping to take this a bit further, and try a more 'world building' genre with a title he's working on. Crime is very psuedo realistic, and verisimilitude is the order of the day. Fantasy on the other hand offers much more creativity. At the very least, it's a fun writing exercise. You'll hear more from Dan on this side project over the coming months, after Morton's return is published this September.
As ever, we'll share results as much as we can.