1) I've removed my airdam (not by choice, I ripped it off off-roading) I personally like the look without it. haven't noticed a MPG drop or stability change. It's just a silly piece of plastic. (I have a 2007, 3rd gen ram though)
2) Leveling kits 90% of the time will not affect your ride OR void warranty. There are the rare cases were a truck just hates the change in suspension but it's rare.
your best bet is to go with bilstein 5100 adjustable shocks as opposed to a spacer. They are just a bit more money, but well worth it. There is nothing wrong with a spacer kit though. (like from BDS, hellbent steel, etc)
bigger tires/level/body lift/suspension lift are the ways to increase ground clearance (for the body at least, ,still have your front diff to think about). For example I went 2" on my level, and 2" bigger in tire size and removed air damn so I'm looking at 3" inches, minus air dam... 6" of added clearance? for the bumper. Your front diff is still in the same spot (unless you get bigger tires). You get 1/2 of whatever increase is tire size you go. So if you bump from 33" to 35" you gain 1" of OVERALL truck height.
Your belt shouldn't get wet without the air dam, or your MPG won't drop noticeably. Sure you won't be as "aerodynamic" as before, but negligible.
Please don't post this a second time in another "sub-forum" it is perfect where it's at.