Disagree, I think Vassell does get involved in games a lot, but like Abe it's mostly off the ball work and covering for the more attacking players.
Goes back to what homer was saying imo. Abe-King-Wellens and Vassell-Yakubu-Gallagher was working so well before we changed it and the reason why was because they all do different jobs compliment each other so well.
King and Wellens have been far superior players this season to last (and have also dropped off in recent weeks when Abe was dropped) because Abe does the "donkey work" (for want of a better term) for them and allows them much more attacking freedom. Gallagher has been a much superior player this season to last because Vassell does a similar thing, they no longer have so much defensive work to do as they did last season, which clearly isn't their strong point, or preferred gameplan anyway (especially Gallagher).
I'm not a tactical theorist so I'm not going to come up with ideas about what system or style we should play, but just going from what I see Abe and Vassell both offer King/Wellens and Yakubu/Gallagher far more attacking freedom and both are by far and away our two most underrated players this season.
When we drop Vassell or Abe (or both in case of the Cardiff game) we seem to lose all balance in the side. Dyer and Waghorn do not offer the same thing than Vassell does, they are too similar types of players to Yakubu, players who like to take opponents on and play off the last defender, not hard-working players who hold the ball up selflessly for the team in the way Vassell does.
Think I'd rather see Yakubu or Gallagher dropped above Vassell, because Dyer and Waghorn can do parts of their jobs (albeit not to the same level) whereas we don't have another selfless forward who covers our other attackers and holds the ball up for them to the what Vassell does.
All my opinion and probably laced in lazy armchair tactical theorisation of course.