When you're a big guy like us, most wheels and tires are going to have some flex or give to them. Don't let yourself obsess on it. If the wheels aren't going out of true then it's just the nature of the beast. Have a good mech check out the wheels before junking them, for sure. A couple of truings on a bike in the first few hundred miles isn't that big of a deal unless the wheel never settles.

Jack is right, if you do indeed break a spoke it's not going to make you crash. I have broken three spokes in one ride home once. Cranking up a long hill one went, then another, then a third by the time I got to the top. The wheel didn't collapse and it didn't make me crash. Of course that was the last ride for that wheel, but I made it home (about 5 miles after spoke death) with no other problems. I didn't realize what that "plink" sound was until I got home or I may not have ridden it the rest of the way but I made it ok.