Shelves with adjustable heights would definitely help, until then try organizing several additional items on each self by placing them in a straight pattern versus angled, because it looks like you could fit more items on 1 shelf than you are currently utilizing. Also try mounting your parts drawer cabinets in another location, like inside a closet so you can use the space of that shelf area to display your collection that is in your stepbrothers area! Your existing shelves have a lot of dead space in between them that could be used if you add a U-shaped home made shelf to have a double decker shelving system providing 2 levels of vehicle storage on each shelf. One word of caution though, be sure to test the shelf's stability because the more weight you add the more you maybe required to anchor the shelves to the wall to keep them from falling. I also recommend that you store the container tubs currently on the your shelves in an area out of sight so your valuable shelves can be used to display your collection stashed in your step brothers area.