2-7 triple draw question

I've just started playing 2-7 triple draw and I have a basic question about playing from the small blind. I'll often play a hand like 38KA10 from the small blind if there is no raise and draw three for an 8 against two players. Maybe I'm wasting half a bet with this call? What about 397AK in the SB? Should I call and draw three to the 7 or two to the 9? I usually toss the 9 in this spot figuring that my opponents are drawing to better than a 9. Maybe I should toss the hand completely? Any suggestions will be helpful.