Is there disagreement over how to calculate VORP (or VBD) in dynasty leagues?
In redraft leagues, the basic idea for VORP is to calculate fantasy points over baseline. You take a player's fantasy points for that season and subtract the number of points scored by the last starter at his position (e.g., RB24). There are fancier things you can do with the numbers, and reasons why you might not want to follow the numbers exactly, but that calculation at least gives you a rough idea of the relative values of different players across positions.
In dynasty leagues, what I'd do to calculate dynasty value is to calculate a player's redraft VORP for each season, and then add up those numbers for every season of a player's career. If you're getting a player now, his dynasty value equals his redraft VORP for the 2011 season, plus his redraft VORP for the 2012 season, plus his redraft VORP for the 2013 season, and so on until he retires. There are fancier things you can do with the numbers, and reasons why you might not want to follow the numbers exactly, but that calculation at least gives you a rough idea of the relative values of different players across positions.
It's hard to estimate the future, but you can also look at the cumulative dynasty value of past players over their careers.
Shaun Alexander gave you 5 elite (top 6) seasons and nothing else, each one worth from 119 to 221 points over baseline (RB24), for a cumulative total of 743 points over baseline for his career.
Marvin Harrison gave you 8 elite (top 10) seasons, each worth from 70 to 119 points over baseline (WR30 is what PFR uses for some reason, so we'll stick with that), for a cumulative total of 786 points over baseline for those 8 years (he also had another 24 points over baseline in 2 decent seasons earlier in his career).
In any one season when both players were playing at an elite level, Shaun Alexander was much more valuable. But Marvin Harrison had a longer career, and was able to accumulate more total value over baseline during his career. It is generally true that elite fantasy RBs don't last as long as elite fantasy WRs (or TEs or QBs), which is why the early rounds of a dynasty draft should generally be less RB-heavy than the early rounds of a redraft.