Why would you fly with a deployed spoiler when you can have a clean aircraft? Sure, there are many canard kit plane designs, but when you look closer at their performance, its is not improved by the location of the elevator. Burt Rutan would always choose a higher wing loading than required to fulfill the FAR part 23 requirements for low speed, so his designs could cruise faster. When asked about this, his usual response was "**ck the FAA!".
When you look closely, canards will give you:
- With natural pitch stability a higher lift coefficient on the forward wing which also needs to have some margin for control surface deflections. Consequently, the big, rear wing is operating at a fraction of its potential when the aircraft stalls.
- The vorticity from the front wing creates a downwash at the mid section of the rear wing and an upwash at the outer sections. The strength of these induced speeds varies with speed, so the main wing can produce an elliptic circulation at only one angle of attack. At other angles, its induced drag is higher than what is possible with a conventional configuration.
- The center of gravity is ahead of the main wing, so the landing gear needs to retract into the fuselage, taking space away from the cockpit. To move the wing center section forward, so it can accommodate the landing gear, the wing needs to be swept (which creates a host of problems of its own).
- There is no good position to put a vertical surface, so again sweep is used to shift some part of the airframe backwards and combine the vertical with winglets. Those need to point upwards, so they do not hit the ground during take-off and landing when the better winglet would point downwards.
Canards start to make sense when they are unstable, but this is not a good approach for a GA aircraft.