hmm... here to throw a few ideas around for discussion
1) i think decorations or not, as long as the tea ware is well understood through use, the brewer can calibrate the brewing to taste. this is not to say that classical shapes will give the best performance in tea brewing.. there is science in the shape, material and all that, but there is also control from the brewer in making decisions (leaf quantity, steep, temp from water dispense), mechanical agitation, and blahblahblah)
2) tea to be judged simply by the brew (in an obsessively compulsive way, that every steep/brew must be "perfect" due to one's subjective tastes), it is a narrow window, and potentially an egoistic pot hole
3) tea as an experience for the brewer, the performance of the pot, history of it, handling, ergonomics, material and the familiarity of the pot effects on tea with sufficient understanding for "full control" over the brewing process.
4) tea as a channel for "aesthetical experiences". recently i posted some videos from some of the "aesthetical tea movements" that had been going on in taiwan for a couple of decades. they can have spring themed tea sessions, pots having decorations of plum blossoms etc.
5) decorated pots are plenty. the poorer reputation for some of the decorated pots stems from the mass production from fake/incorrect materials, in an attempt to get tourists to buy a souvenir based on the looks (most tourists wouldnt even bother whether it is real yixing or not!)
but there are very lovely decorated pots, many of them are big. if you talk about small pots, in the 70s and earlier, mostly traditional geometric shapes. fancy decorations and shapes mostly were on large pots.
only into the 80s when artistic freedom was more available.. do we see small pots that are nicely decorated.
6) there are a lot of very high end decorated pots, beyond the price of the average consumer.. if you go to 紫砂新韻 on facebook and many other groups..
