Every situation is different.Obviously weak walls must be considered,having done both to properties and with good results either time . I know the pleasure of chiselling tiles off a georgian lathe and plaster wall-,total destrution! Only the question will know if the job will look crappy or not ,agreeing with you in many respects,it can be done successfully and with undetectable finish.
As a professional remodeller, it would be unthinkable to tile over existing tiles. Who knows what's going on behind those old tiles, and what kind of backing they have? Do it right, strip down to framing and install a proper backing board. Like someone mentioned, a sloppy job will cost you in future when you are selling.
Yes you can, as long as the original tiles are sound it won't be a problem at all. Make sure though that you leave plenty of time for the adhesive to dry and not grout to soon. If you grout to soon you will trap the moisture in and it won't cure properly. If your walls are plasterboard and you do try and remove the tiles be prepared that if they are stuck on well you may need to replace the plasterboard before you can re-tile. good luck