I too have a really tough time managing Omega items blocking my ability to continue collecting them because they can't be sold, other than the Adviser who pops up and says, "Hey! So-and-so city would like to buy 'x' item(s) for ___".
I am beyond tired of having to bulldoze existing Omega buildings just so I can try to cull through my existing stash if items by refreshing over and over until I find some item(s) to use that I'm not trying to apply to something like increasing Item Storage or my NeoSimoleon Bank cap.
I'll voice that the NeoMall is a price rip off too. I'm not sure as to the logic behind making it so highly expensive. I'd think that since we have no way of selling Omega Items, so that we may continue to fish for them via the OMEGA Research Center, lower prices on Omega Items in the NeoMall would create a better opportunity for higher usage of items to assist in the city building process, but I guess that the devs would rather we struggle? Yeah, seems so.