The level of Stampida's roughness depends on where you sit on the train and even which track you're on (red is smoother, although, you'll probably ride both to get the two creds). If you sit nearer the front and in the front half of a carriage, then it's not too rough, but as with most woodies, the ride is considerably rougher towards the back.
Grand National is awful in the very back row and Stampida can sometimes match it, but I usually quite enjoy it (my tolerance for wooden coaster roughness is quite high though). I can't remember the last I rode in the back because on my last couple of visits they've had the back rows taped off, so no-one could ride in them; take from that what you wish :wink:
I don't know what the re-tracking has done because that's just happened very recently, but I can only imagine there has been at least some improvement in terms of smoothness. Basically, don't go expecting a smooth woodie because it's not and don't expect any airtime because the Kumbak trains have ruined any opportunity of that pretty much. It's decent fun in most places, but if you're allowed to choose a seat, try and get a seat closer to the front for the likelihood of you enjoying it more there.