Gloe, I think that your idea is great. The chart clearly shows that 2008 is different than all the other years. I think adapting MACD > 0 as a VTO filter makes a lot of sense.
It looks like there might have still been a buy or two in the May 2008 time frame that could have turned out bad, but one bad trade is much better than a year's worth.
As far as missing the rally off the bottom, I don't see that as a problem. VTO is not designed for rallies. VTO is a hit and run strategy for pullbacks.
However, I have noticed several times that by the time VTO gets to a sell signal all the normal indicators are saying buy, so in reality VTO can become a great swing strategy to catch the bottoms when nothing else sees them and then stay with the rally.
I also have a weekly chart where I use two different MACD's, one for selling and one for buying that works pretty good. I have adopted the strategy of being slow to sell, but faster to buy. This avoids a lot of whipsaws and gets one back in the market fast after a sharp dip.