I wasn't trying to imply that a 30" printer is a waste of money. Just make sure you look at what you produce, could produce and the future. Large printed banners are very profitable and a lot less labor than cut vinyl. Installing tiled graphics adds extra labor, potential for misalignments and reprints.
Also be aware that if you buy a 24 or 30" printer, the printer won't print to the edge and you will lose 1.5" to 2" . It's also difficult to track perfectly straight when printing and laminating so you need that waste anyway. The registration marks for print cut also eat into your printable area. I am not familiar with Mamaki printers but on a Roland 51.5" is pushing it on print cut mode. So that is like 21.5" on a 24" printer and 27.5" on a 30".