hrbngr: That's called rebalancing. It's not a bad strategy. However, the key point of rebalancing isn't to make more money in downturns, but to keep a stable portfolio for your needs. It's about risk management.
If you want to rebalance just for the money... I believe you'd be better served by investing in 100% equities and letting it ride for several decades. Not just because it's a pretty sure way of having more at the end of the day, but also for mental health: you don't have to worry about whether right now is the right time to rebalance to get the most money, but what if the stock goes down, let me keep track of this and refresh every day, blah blah blah, blah...
Do you see what I'm saying?
With that said, your plan is certainly workable if you're willing to lose a little bit of sleep. It may or may not be more profitable. If you think it's a good idea, go for it -- just remember not to panic. If you can avoid panicking, you'll be ok in the end.