Wow, I'm honored to be part of your DVC decision. Being members of the Disney Vacation Club has been a wonderful investment for my family. I hope you enjoy it as much as we do.
I'm not sure when in the spring your trip had been for, but a great time to be at WDW is the last week in April and the first two weeks of May. The crowds are on the low to average side and the weather is usually fine -- not too hot, not too rainy. Once you hit the week before Memorial Day, both the crowd level and the temperatures heat up and will stay that way until mid-August.
If you need to travel between Memorial Day and about August 17, I don't think it matters much which dates you choose, as you can expect similar circumstances throughout that period. The only exception to this would be the week including July 4, which will be even more crowded than the rest of the summer.
My family's DVC points use year also has an August 1 start date. When we have been in situations like yours, we have occasionally rolled points forward into the next use year. If you were willing to do this, you may find that travel in the fall is your cup of tea. The entire months of September and October have low crowd projections. If you made a trip in the fall of 2009 and then again in the spring of 2010, you'd be back on schedule. You could also capitalize on having two trips in a 12 months period and purchase an annual pass. I have done this many times and ended up saving not only on tickets, but also on tours and dining by taking advantage of the annual pass discounts and the
Tables in Wonderland card.