I have a Brinkmann 4-burner propane grill.

I replaced the ignitor and the ignitor burner lights fine.

But the others do not, I have to use a lighter for those.

Second item.

The flames coming out of the burners are uneven, so I think they need to be replaced.

I can not find the model number on the grill.
Anyone know where Brinkmann hid the model no. :-)

Is it worth buying 4 more burners or go for a new grill ?

You could always got to Brinkmann website and contact them. Ask them for the model number location. Regarding your financial decision I can't help you.

Throw it away. Buy a Weber.

On all counts, it sounds to me like the burner-assembly is probably just dirty. Lots of stuff drips down there. If the assembly can be removed, e.g. with screws, I would remove it and clean it thoroughly. (One somewhat-clever way to help do that is to use a propane torch, having first removed it and laid it on some non-metal surface such as a pile of (fire...) bricks. Wear flameproof gloves and eye protection. Heat it up so that any residue that might have slipped into the tubes will be carbonized. Soak it in a small amount of water to which drain-cleaner has been added. Rinse thoroughly and let it dry for several hours in the hot summer sun.

You can order spare parts from the manufacturer for any unit, even comparatively older models. I see no reason to pay "dealer mark-up" twice on something as technologically simple as a propane grill ... but, I'm cheap that way.