I used a fair amount of 'noids back in the day, fortunately never anywhere near to the extent of becoming addicted though. As you say they generally weren't pleasant, and set off irrational / intrusive / paranoid / anxious / racing thoughts really badly.
Why I persisted, God only knows. Perhaps because I had paid for the powders, made my own smokeable mixes using acetone to spray the noids onto smokeable herbs.
Very late in the game I discovered that noids are actually fantastic when combined with GBL. GBL was the only thing that eliminated and tamed the negative psychological side effects of 'noids for me. Music sounded fantastic, a whole new semi-psychedelic listening experience was opened up, and that was very enjoyable.
Unfortunately around that time the laws on GBL changed and it was no longer easy or grey area legal to import the stuff from Germany for cleaning your drains or alloy wheels.
I bought loads of noid powders ridiculosuly cheaply in the fire sales as their ban date was looming up. I cant remember exactly but it was something insane like 50g of pure powders for £10, and that would go a very very long way and last decades potentially. I think I bought about 3 different types. But without GBL they were no good, and I ended up pouring the whole lot down the drain in the end. So to be relevant to the thread title, buying all those noid powders in insane amounts was definititely a mistake, even if they were dirt cheap. But that was far from my worst drug mistake(s) I've ever made. I think I've mentioned some of them previously in this thread.
The ban, and then the fire sales, were almost certainly what caused the "spice epidemic" that broke out shortly aftwerwards in many cities and towns. Dealers probably buying tons of the stuff dead cheap, (the vendors were practically giving the stuff away by the end, they must have had trouble shifting it,) and selling it on mainly to the homeless population at cheap prices.