依Wikipedia上查到的資料
VORP是有根據ball park來做調整
wikipedia
Before calculating the VORP, the individual player stats must be normalized via park factors to eliminate the distortions that can be created by each ballpark, especially extreme parks like Coors Field in Denver (where the thin high-altitude air allows baseballs to travel further than at sea level) and Petco Park in San Diego (where the heavier sea air couples with distant fences to suppress run-scoring). After the final adjustment, the resultant VORP may be used to estimate how "valuable" the player in question is by providing a good picture of that player's marginal utility.

至於時空的問題
因為這數據本身就是根據當年的替補球員level來做的
而最後得到的是這個球員比替補的水準高多少
我覺得他就是一個水平
所以應該是可以反映不同時空的表現

當然也有人認為VORP被過度使用
Overuse of VORP
而且VORP沒有計算到防守的部分