I agree about the cape for gohan. Looks good but way too limiting.
In regards to MIB collecting, I don't really do it, but here and there i keep a few piece in the box, usually ones that don't offer much in terms of articulation of accessories... Neca comes to mind, though I don't own much neca. I will say though that figuarts look great mib. The plus side is you can put them right back in after opening and the only thing lost is a seal of tape. But there is another side to mib collecting than future profit.
The idea of something being new is one we often all strive for in life. We want new experiences, to meet new people, go new places. We miss our childhood because back then everything was new to us. One of the most tragic devices in storytelling is the loss of innocence, which in a way is just the loss of perspective that new things can be perfect. A MIB figure is something that, when kept that way, is untainted and will forever be new and fresh so long as it is maintained. To me, that's where the allure comes from. I've felt personally, and seen from others, whether they are aware of it or not, a pretty deep psychological connection to MIB.
Of course, ultimately those are really just projections we place onto figures, and is not all that different than the reason most adult toy collectors exist, to recapture something of their youth, so I forced myself overcome the compulsion to keep figures in the box and allow me to enjoy them. It's much more fun for me that way, but once in a while I have a harder time bringing myself to open something and when I think why that is, I often come to the reasons outlined above.