I ran a SN1/HC from 2007-2021 and it was a solid performer. The SN3 was to my ears a good improvement in air and detail and just more lovely sounding BUT I concur with previous post that SN1 was better in some ways. SN1 was a more solid chunky ‘fun’ sounding amp and while not as ‘hifi’ as SN2/3 was sort of special in its own way. I wish I had kept it for a garage system or other. SN2/3 are much closer in sound to my ears, if you have a 2 I would not recommend swapping to a 3 unless you were running a TT with a MM cart (then the SN3 has a great inbuilt phono to utilize).
Side note. I have had my SN3 about 6 months and have not as of yet added the HC to it as it is on a shelf waiting to be recapped and just have not got round to doing this yes, all parts are here, I just need to find time!)