If you plan on printing full vehicle wraps with a 30"... Id say no.
It won't even be wide enough to do a door without a seem... You can get away with seeming certain areas, but if you have to seem every door, the hood twice, trunk twice, it'll look like a hack job.
If you're just printing decals you can get by with a 30". You'll be wasting more material... If someone wants a 16" decal you can't put 2 side by side, now you have almost 50% waste. So you're more limited, but you can get around that by running promotional items / other stuff along side it.
Walls your fine - when we have a customer buy a wall wrap and want to install it themselves, we split it up into 26" pieces so it's easy for them to handle. yes, you get more seems... But there's a reason most wallpapers are in small under 30" rolls... I doubt any customer could put up a 52" panel and join it properly.
Most people who have a 30, or get a 30, end up upgrading very quickly because the 54 is more convenient and cheaper to run.
Do you have a laminator? Finding a 30" laminator is somewhat of a pain too, unless you go manual.