First, I wouldn't trade Valverde unless you feel that you are getting a potential franchise type starting pitching in return (like a Matt Cain or Phil Hughes).

Second, I don't think Maine and Schneider are sufficient return for Valverde. Schneider is more similar, than dissimilar, from Ausmus. He had a decent offensive year in 08, but his offensive numbers in Washington were similar to Ausmus (Ausmus and Schneider had nearly identical offensive numbers for 07...BA in .230's and mid-.600's OPS). He is similar in age, meaning we can't expect an upside, and is a decent defensive catcher. Nothing wrong with that, but if people are expecting an offensive force from Schneider, you may be disappointed. Maine is coming off season ending shoulder surgery. The surgery may not be all that serious, but it is a concern, particularly for a pitcher who succeeds without particularly great stuff.

Third, I think people underestimate the size of the hole created by Valverde's loss. After you factor in the cost of replacing him, you may not end up gaining much from the trade. A significant reason (IMO) for the improvement between 07 and 08 is the difference between the terrible closer situation for the Astros in 07 vs. the more stable closer situation provided by Valverde in 08. Hawkins'is well known as the prime example of a player who is only good as a set up man and always fails as a closer. Going into next season with 42 year old Brocail as closer would be madness. So, the Astros likely would be forced into the free agent market to complete for a closer like Fuentes, who is likely to cost $10 million or so. That means you end up paying more and getting less, than if you kept Valverde. Maybe that is worth it if you get a prime young ace starter...but I can't think of the right match with a team which is desperate for a closer.