exhaust brake is a "nice to have" item...not a critical item for such a small trailer.
If you have no indication of a problem you should easily get another 100k miles out of the truck if not a lot more.
But...when it does go, do look at 3/4 or 1 ton trucks, they aren't significantly more expensive than 1/2 ton trucks, so you don't need to downgrade the truck. We just picked up a nice 3/4 ton 2008 for under $10k and the prior one we sold after 5-6yrs was $5k. Never had any repairs beyond normal maintenance (brakes, shocks, oil changes)