that depend, you must seek the cause compare with other products in the market. (for that, you must known how many sales have others)
and this is basic, if its because price high compare with other similar products with more sales and/or more quality, you must lower, you got less profit for each sale but you going to sell more attracting more costumes with less budget. if its because its very specific content for very specific users you must increase. (of course quality matters in this case more)
or perhaps your work ins’t good enough.
ATM you can’t know the interest in certain product or how many buyer have the UE4 market. Unity at least have the “Top seller” and the ranking, votations,etc to get a idea.
the market more profitable still google play, steam and that with lower prices, of course we can’t compare, they have a millons audiencie, you can’t sell something to 1$ wanting making 1.000.000 sales in the ue4 market. i think i don’t known how many users have UE4 and that another problem… because you “Material pack selling at 1$ perhaps make more money than 20$ if there are ue4 user enough” who can’t spend 1$ its 6 nice materials? (i don’t think so anyway, its a example engines are no something that isn’t widely used)
A good tactic its perhaps make your first “material pack limited” FREE, known how many are interesting (if you can look at stadistics) and adjust the price for second.