Nick speaking,
About five years ago, you would hardly ever see my Eye of Terror Space Wolves 13th company on the table, in actual fact if I hadn't put so much time, effort and money into converting them all, I probably would have sold them off by now. With the lack of vehicles and an aging Codex compared to the new shinny editions, I started to lose my enjoyment for them.
Back in those days I was mainly playing against Blood Angels, and that was probably the real reason for my lack of love for these guy's. With their fast moving Jump packs, horrible Death Company and Honour Guard units, it was always hard for me to control the game, especially without any vehicles! When you coupled the BA fast movement with furious charge, close combat was always a problem for me, even though I was a CC army?
So for a while I shelved my Wulvenkind in favour of my Necrons, but when I got my copy of the first GW 'expansion book' Cities of Death in 2006, it occurred to me that my 13th Company could make an ideal army for Cities of Death! With all the buildings around I could avoid being shot at, and so giving me no disadvantage in not having vehicles! So with that inspiration, I got started on my Ruined Buildings terrain...
The Cities of Death Codex was the first inclination of where GW was going with fifth edition, as it was here that we saw Troops only as scoring units for the first time, and this was ideal for my Wulvenkind. I no longer had to take my points heavy ten man units to try and walk across the board, I could take several five man units and sneak them around the heavy terrain claiming objectives!
I suppose the long and short of this post is that different scenarios and missions can have a big impact on your armies ability. Back in forth edition, GW gave us all the extra scenarios for free, but now they sell them to us in the form of 'expansion books'.
I have not gone down the route of 'Planet Strike' or 'Battle Missions' yet, but If you are starting to get a bit fed up with your army for whatever reason, just get a few of your willing buddies to give something else a try instead of the three standard missions, and you may just get some love back for your army again...