Unlike child support, spousal support is often very difficult (if not impossible) to modify after the divorce is final, so getting it right the first time is a must!
This happened to a friend of mine. Divorce was final one day, the next day, he & about 300 of his fellow employees were dumped from their very high paying tech jobs at a large, well=known company in town. Very few of them had college degrees because they were in specialized areas that had more interested in thier expertise in THAT company's stuff than having a BA or BS.
So my friend almost immediately found himself unemployable... actually, several of my friends from this company found themselves almost immediatly unemployable, but this one had just had a child support amount set for his relatively high income.
Some of the guys had enough seniority that they had enough severence & were able to go finish up college & start teaching secondary school in decent second-career type salaries... a very few were able to get jobs in competing companies. My friend decided to start a consulting firm, and over the years it didn't turn out very well.
He had to ask for a child support modification right away. He won. His company's downsizing was notorious in the city & no one in thier right mind would expect him to turn around & make the same amount of money right away.
I expect your situation will be the same. Everyone knows of the downturn of the residential real estate market over the past few years. You'll want to point it out so it's on the record, and explain that this is why your income has decreased, but I think the judge would find your explanation reasonable.