The things that make for a good road wheel aren't really all that different for a 'cross wheel. In either case, you're looking for something well built, as light as is reasonable given cost and reliability constraints, and individual components that can handle the required task.
In the case of your RS10s, I think you'll likely be fine. Shimano's wheel build quality is quite good, the hubs are pretty well sealed (and easy to work on if they do get contaminated), and the relatively shallow rims should make for a decently comfy ride over the rough.
They're perhaps a little heavy for a true race wheel but that's neither here nor there as far as I'm concerned. Believe me, I've been smoked on many an occasion by someone on a far lesser bike than what I'm usually privileged to ride simply because they were fitter and faster. While I still say that the rider on the better bike will be faster *all other things being equal*, there's no substitute for the engine.
Get yourself a good set of open tubular tires if your budget allows (such as ones from Challenge) to maximize what those wheels can do and then upgrade later as your skills, fitness and budget improve. If you find that you really love the sport, keep your eyes open for a set of used tubular wheels in good shape. In 'cross, the biggest improvement you can make equipment-wise is by switching to tubulars as they allow for far lower operating pressures than even tubeless clinchers (I ran 26 and 28psi front and rear in my race on Sunday), letting you roll faster, corner much harder, and finish fresher.
In the meantime, get out there and enjoy the suffering.