Levers won't make much difference
In my experience, the Deore Mechanical Disc brakes aren't the strongest (my buddy has them and thought mech discs were a gimmick until he tried my Avids and did a endo and just about ate it!). The Avid levers might help the modulation, but honestly you be better off keeping the Deore levers and investing in better calipers. When it comes to mechanicals, Avid wins hands down (the "high end" Hayes MX1 mechanicals are better than the Deore's, the MX2's are about equal...but both are still well below the Avid's). Larger rotors will help, but by the time you invest in the bigger rotors and adapters, your already halfway to a set of Avid's. Combine that with the money you'd spend on new levers and you have enough for a set of Avid BB5's
Good Luck