Strongly agree, the slow thermal diffusion limits the Sterlings in yield, which explains the helium or the hydrogen (dangerous, but 3,3 times more in distance D = 160 to 190 mm2 / s) and the use of stacks finely divided, because the diffuse air of 4mm in 1s (D = 19mm2 / s) and therefore so fast, it takes dimensions as square root of time, 10 times smaller for 1 / 100 second, 0,4mm actually 300 Hertz because there is the factor Pi = 3,14 in the period formula on Pi, in the root of D).
http://en.wikipedia.org/wiki/Thermal_diffusivity
http://fr.wikipedia.org/wiki/Diffusivit%C3%A9_thermique
http://fr.wikipedia.org/wiki/Conduction_thermique
So it is essential to divide finely, without necessarily putting a multitude of pistons, finely divided heat exchangers, stacks, may be sufficient, such as thermoacoustics, which by wave, impedance granted, compensate dead volumes, if well designed. (similar to microwaves, but not simple in comprehension)
We must be able to combine thermoacoustics, and Stirling to have the advantages of each and to reduce the inconvenience, with displacer piston and work fast, remaining simple.
In very low temperature cryogenics, this is commercially expensive, even at NASA.