I've always thought the main point of the 'limited' DG (diatonic) melodeon is the built in rhythm section it provides- great for dancing, not that I do much of that.
   'English' and Scottish music tend to use much more staccato rhythms (the Scotch snap etc) and the melodeon provides this in spades. The piano box is now the norm in Scotland- some folk seem able to have a technique to replace some of its lost rhythm capability, & it's done mainly by drums & bass. The DG melodeon is dominant in England of course but the semitone tuning favoured in Ireland suits the much more ornate & flowing nature of Irish dance music.
    Attempting to 'smooth out' the DG melodeon for playing reels by crossing rows is OK- I do it myself, but also reduces its innate rhythm. I grew up with Irish music & did try the BC Paolo for a while but not for me as a singer too.
    As for the bass buttons on two-row diatonic boxes, I watched fascinated as Tim Lyons played his BC box & tapped the totally unrelated bass buttons as well as the melody side. I asked him what he was doing with it &he said 'jaze I dunno, I look the other way'
   another rated Irish box player did similar & said 'ah but it's only percussion anyway'    nufsed