Yeah in the same boat: nothing interesting to buy there…
There was this thread or this one… but no reply of devs…
It seems that purchases or not purchases is out of the devs’s hands and maybe are in the publisher’s ones…
Personnaly, I will like some customisation like the leprechaum skulls, why devs didn’t put a 5$ pack? Or this one (it was like one month that I didn’t post this link 
).
But @Saltypatra may we know what it blocks putting more stuffs in the shop? Lawyers again?