I think that nutrition bars are good as supplemental meals or snacks...but not that they will necessarily increase your mass, strength, etc. Some are marketed as such, but that's just because they pack the various supplements into that FORM to take.
The best bars for snack substitutes or even meal replacements (better eat 1 1/2 or 2 though) are the ZONE PERFECT bars. They have more protein in them than almost any other bar I've found (like, 3-5 times as much) and they taste like candy bars. They are well balanced on fat, calories, and protein. Best of all, they are one of the cheapest to buy as well...about $1 each.
If you need to load on carbs, then I would suggest buying a supplement like Weight Gainer or something and make the shakes. Whey or Soy protein made into shakes is good too...I prefer to stack the protein more than the carbs because I am not trying to "Get Big" just endurance strength.
Just my humble non-expert opinions.