All the bets have about a 1% house edge. Betting <1 every time will cost you about 1% of everything you bet on it in the long run, whether you're making other bets at the same time or not.
SatoshiDice used to let you make multiple bets per roll, but they stopped allowing that back in January - presumably because allowing multiple dependant bets gives people a way of effectively exceeding the max bet. If I'm only allowed to bet 1 BTC on <32000, maybe I can bypass that restriction by putting 1 BTC on <32000 and another 1 BTC on <32001 on the same spin?
So long as the site is careful to limit its total exposure per roll, taking all bets into account, I see nothing wrong with allowing it. But it might clutter the interface if not implemented nicely.
Just have each separate bet deplete from the maximum allowable bet. About the clutter I thought that also, and there's ways around that such as leaving the default betting screen how it is now, and allowing someone to select a different screen with the more options if they want.