baranfin,
Don't think of stub wings, call them wings. The lift gained at high speed is significant, and unloads the rotor so that stall is averted. Winged helicopters can gain 20 knots top speed, or so.
The weight is a penalty, but the vertical drag is eye-watering. The typical helicpter vertical drag (which "feels" like weight, and subtracts from hover performance exactly so) is about 5% of gross weiht, so a 20000 pound helo loses 1000 pounds of payload due to vertical drag. The wing can easily add another 5 to 10% vertical drag (the V-22 wing probably costs about 8%), which is an awesome penlty. Since typical helicopters have payloads that are 40% of the maximum gross weight, a loss of 10% of gross weight costs 25% of payload.
Pivoting wings, big flaps that dump down in hover and many other schemes have been tried. Since the wing is an important structure, any scheme must be completely fool-proof or a catastrophe could result.
Stepniewski and Keys "Rotary-Wing Aerodynamics" has a whole chapter on winged helicopters.