slowrotor,
Please don't apologize for being negative. Criticism is desired. It instigates the the evaluation of potential defects.
The following are responses to your three concerns. Hopefully, they will satisfy your objections or solicit further criticism.
- Speed: You are no doubt correct in that high speed serves little purpose for very-light rotorcraft. For large rotorcraft however, it probably is very important, since it increases the envelope of usefulness. The effort that is being put into the V-22 supports this belief.
- Lateral symmetry: (Only for the non-religious.
) Darwin's theory of evolution has shown that in nature, only the successful survive. It must be noted that virtually all 'mobile' forms of life have lateral symmetry, be they; in the water, on the land, or in the air. Since most of mankind's inventions have their foundation in nature, it understandable that man's 'mobile' creations have lateral symmetry also. Again, consider the vessels in the water, the vehicles on the land and the craft in the air. IMHO, the motorcycle sidecar and the single-rotor helicopter are aberrations. 
- Rotor Induced Vibration: A valid concern. Research is currently being conducted at universities etc. to try to reduce vibration, and its Siamese-twin, noise. The ultimate successes will be twice as beneficial for twin rotor configurations.
Dave