Since the mission rewards are pretty openhanded the clintz-per-credit value of the solo missions is pretty much same as average pack value, maybe slightly less because you can optimize packs - but then again those mission prizes are guaranteed so they have no "bad luck Brian" effect on them either.
So in conclusion: It is neutral choice. Do as you wish, its not fail in either way.
For me, single player mode is really fun, so I don't mind to open it
however if you don't like it, the don't open it
their locked levels have some pretty fun stuffs, like fighting a T2 deck with ELO deck, a deck with all level 2 cards, etc
it is challenging esp if you don't have the resources to counter opp deck (like having Piranas against pesky Montana)
P.S: hmm.. did they update the deck using the latest card? the enemy is not as scary as before..
buy the omega levels if you like single player mode, they are very challenging..