Agreed that underdosing can lead to a somewhat uncomfortable and indecisive trip. That applies to most psyches, I'd say, but as aMT tends to have quite a strong physical element (the stimulation in particular can be pretty intense, but there's also the GI issues for those unfortunate enough to get those to any significant extent) underdosing tends to leave you in the worst of all worlds: all the physical effects, fewer of the mental and emotional effects that put it all in context. It just feels a bit weird and confused much as you describe, Dan.
It's very much in the YMMV territory when it comes to dosage too. Some people will get full effects at 30mg (or even less than that) whist others will want twice that amount - or, in some cases - significantly more than that (triple digit doses are not unheard of but obviously are not the place to start for anybody). As long as you're not combining it with any other drugs at all, aMT itself seems to be well-tolerated at a wide range of doses. The stimulation tends to level off as the dose rises - past a certain point you will be very stimulated but probably not vastly more so than at a lower dose. It's more the psychedelia side that intensifies as the dose rises. Somewhere between underdosed frustration and high-dose intense psychedelia lies a happy medium where you get the full, MDMA-esque euphora, empathy and energy (a bit (or even a lot) speedier-feeling than MDMA itself generally speaking) with a smattering of psychedelia which usually becomes more noticeable around half-way through the total duration.
It's also worth mentioning that there has been some fairly significant variation in potency between batches. I'd not like to hazard a guess as to why but I have heard that it doesn't store so well unless under optimum conditions which may have something to do with differences in potency or it may not. Either way, I'd say it's best to find which dose works for you afresh with each new batch and don't rely too much on the doses others report as they may have a significantly stronger, or indeed weaker, batch than you do. If 30mg was underwhelming, and this is from the same stuff you used before, I'd maybe go to 40mg next time and see how you go. 50mg is unlikely to be a problem but is obviously quite a big jump up from 30mg. As psyches go, aMT is one of the "easier" ones as it tends to come with built-in, near-guaranteed euphoria and positivity, as such it's a good choice for people who like the idea of tripping but are maybe a bit wary for one reason or another. Dosing a bit high is perhaps not such a risk of a "bad trip" but it is certainly a full-on psychedelic at said higher doses. If not so sure about whether the psychedelic side is what you want the emphasis on then I'd suggest not jumping up in dose too much as it's nearer to an MDMA-esque, entactogen-type experience at sub-psychedelic doses.