You could apply your logic to morphine or heroin. You could say "Well, I tried it a couple of times and it made me sick so clearly that is what the drug does and will always do and therefore it is a shitty drug." But in reality opiates only fuck with you like that when you meet them for the first time and then, like with DXM, your body/mind becomes used to the transition and it ceases to be unpleasant.
I get you now, that comparison with opiates makes sense, having gone through that with opiates myself and feeling ill the first couple times then eventually feeling no sickness and just the positive effects.
I only tried DXM a couple times and I was sick for most of the experience, threw up alot. Never dosed higher then 600mg, but in terms of the positives I did have that weird/disconnected feeling from reality. Visually I didn't have any OEVs but my vision would 'trail' if that makes sense, like I would look ahead then as I'd turn my head the prior image in my brain would have to 'catch up' to what I was now looking at making my vision like a really old film where each photograph was a second or so apart making the film appear fragmented, though thats not really the right word, but I'm not sure how else to describe it. I'm sure you would understand though. The visual 'trailing' was very different to that of psychedelics like LSD, where the trails occur in a more flowing manner.
I'd have strange thoughts no doubt due to the weird and disconnected/disassociated aspect to it aswell. And alongside all that I had this sort of drunk, giddy euphoria which was decent. Obviously I also felt the changes in depth perception and robo-walk effect, which made walking downstairs difficult but it all just seemed funny at the time. Nothing profound or incredible was experienced though, and by the way alot of people seem to describe the 3rd and 4th plateaus I guess I never brokethrough to those levels.
But having said all that, the nausea and vomiting was heavy and lasted throughout the experience, though I do have a naturally weak stomach which would have added to it. Also drinking the what felt like a large amount of foul tasting cough syrup didn't make it worthwhile. Especially when other drugs I would prefer to spend my money on are/were available.