A combination of patience and aggressive trading is the key.
Since most veteran players generally reach their targeted levels (give or take a little, and barring injury, trade, etc), you are better off keeping Sexson and hoping for a rebound (he has hit .320 with 3 HR and 9 RBI in the past 7 days).
Your idea of trading some of your pitching for some hitting and relying on the WW to improve pitching down the road is a sound strategy, I think. There always seem to be pitchers of some worth on the WW in all but the deepest of leagues. Get some proven bats to bolster your offense, and keep a keen eye out for pitchers showing improvement, getting called up, or facing a favourable schedule.
George Bell 1987 AL MVP
"Kiss my purple butt."