You have Randy Johnson, Pedro Martinez, and Curt Schilling?
I think Santana is going to have a great season and he has a fantastic upside both for this season and longterm in a keeper league. Many people haven't given him a close enough look. He's had better than 9K/9IP for the last two seasons, and went 8-1 after being named a full-time starter after the all-star break last year. In 2002 only your very own Randy Johnson had a better K/9 out of any pitcher that threw at least 100 innings.
Smoltz worries me, and with Johnson, Schilling, and Martinez as your keepers, I wouldn't add any grizzled old vets.
So for me that changes your question to, should I release Santana in the hopes that I can get Schmidt? If you are higher on Schmidt, and think if Schmidt is gone, Santana (whom you've now released) will most certainly be around, then I'd do it. If your not as certain as possible that if you cut Santana lose that either he or Schmidt will be available, I'd quit while I was ahead.
Me, I wouldn't gamble. I think Santana will be great this season, and for seasons to come.