Yup, in theory you can get everything from Recruit packs, but it's a long process of eliminating all the commons and uncommons first. The Veteran and Spectre packs just allow you to skip ahead a bit and grab a few rare and ultra rare items ahead of time. One drawback of saving up for Spectre packs is that you will not have a steady flow of medi-gel and cobra missiles, where as buying 12 Recruit packs instead would give you a ton of those one-use items.
I'm still having a lot of fun experimenting with different builds. This is something you really can't do in single-player as easily, due to the massive time investment to get Shepard to higher levels. You can also goof around with fun tactics and try out oddball combinations.
While playing my Quarian Infiltrator, I had a lot of evil fun using sabotage. I would walk towards a Nemesis sniper, in the open, and when they aimed their rifle at me I'd sabotage it. While they tried to fix their overheated weapon, I'd omni-tool them in the face. My next infiltrator will be a melee build, for fun and experimentation. Take a shotgun with bayonet, take the Tactical Cloak talents that improve melee damage while cloaked, and max out Fitness for more melee damage bonuses. Sneak up on enemies, assassinate them.