First rounders are worth hanging onto at into their 3rd season, and I'd try to hang onto second rounders at least into their 2nd season. Beyond that it depends on the specifics (as FantasyTrader says).
Looking at averages, here are some numbers for WRs drafted from 1993-2006 (using the data from
this post). 40 of the 56 (71%) WRs drafted in the first round during those 14 years were fantasy relevant at some point in their career, meaning that they finished in the top 36 in at least one season. If we define a breakout season as the first season in his career when a WR made the top 36, 23% (13/56) broke out as rookies, 26% (11/43) of those that did not break out as rookies broke out in their 2nd year, 38% (12/32) of those that did not break out in their first two years broke out in their 3rd year, 15% (3/20) of those that did not break out in their first 3 years broke out in their 4th year, and only 6% (1/17) of those that did not break out in their first 4 years ever broke out; the other 16 WRs never broke out (although Mike Williams still has a chance). Here are those numbers in chart form, along with the numbers for 2nd & 3rd round WRs:
year 1st rd 2nd rd 3rd rd1 23% 12% 4%2 26% 17% 12%3 38% 14% 9%4 15% 8% 5%after 6% 6% 0%One problem with the definition of breakout that I used is that it says that Todd Pinkston had a 3rd year breakout (since he finished as WR30 that season; he never again made the top 50). What if we only count breakout players who have some real fantasy value? Here's that same chart, where a season only counts as a breakout if 1) the WR finishes in the top 36 that season, and 2) the WR accumulated at least 50 VBD for his career:
Code:
year 1st rd 2nd rd 3rd rd1 20% 7% 2%2 16% 10% 6%3 22% 5% 5%4 0% 5% 3%after 6% 0% 0%