My 0.4m f/6.5 + SBIG8 has an image scale of 0.73 arcsec per pixel, and a Airy disk radius of 0.35 arcsec (equal to the Rayleigh resolution limit); typical seeing is around 2.0 arcsec. The Nyquist criterion is that the detector should have at most half the size of the desired resolution. On this basis, the seeing-limited image is (just about) adequately sampled but the diffraction-limited image is woefully under-sampled. Each of lucky imaging and deconvolution allow resolution beyond the seeing limit.
The above suggests that a Barlow or equivalent which extends the effective focal length by a factor of 2-4x could be useful. Such devices in 2″ format are moderately pricey and I’d welcome recommendations before buying anything.