Most draft picks are worth less one year after being drafted. Of course there are exceptions if a prospect has a bigger year than expected and is looked at as a better prospect than he was on draft day. But generally speaking a team would rather have the pick cause they can select the player they want, position they need, etc; rather than a locked in prospect. Comparative value of the draft is a factor too and like I've said here a few times, next year will be a better draft than this one.
But the biggest factor is how they perform. For example Michael Hage is probably worth a bit more than the 20th pick where he was taken cause last year's draft was better and he had a strong rookie season with Michigan.
A guy like Mesar on the other hand, he had a poor 18 year old season with Kitchener, and was worth less the 25th pick one year after he was drafted.