As the first answer notes, some people like doing yard work and others don't.
But beyond that are at least two factors. The first is: Is the back yard more usable and thus more desirable than the other back yards? Does it offer a practical advantage? Would someone look at the other back yards, then yours, and say, "Wow. That's a really nice back yard." If that's the case, then the back yard does add value that the other homes don't.
The second factor is: How much larger? It's true that larger lots usually justify a somewhat higher price. Maybe not a lot, but some. Example: If your house is on a 15,000 sq. ft. lot and all your neighbors are on 14,000 sq. ft. lots, that's not much of a difference. That alone probably wouldn't affect your value at all. On the other hand, if your house is on a 30,000 sq. ft. lot and all your neighbors are on 14,000 sq. ft. lots, then that's a big enough different to affect the value.
And of course that's assuming that the houses are otherwise identical. If your neighbor with a slighly smaller lot recently upgraded his kitchen and baths while yours are 15 years old, your neighbor's house might sell for more, even with the slightly smaller lot.
And one other factor: Back a few decades ago, corner lots were considered more desirable than lots that weren't on a corner. That preference has shifted in many areas, so that corner lots are sometimes considered less desirable. If that's the case in Humble--and I don't know if it is--then maybe the lot size or back yard matter less than whether you're on a corner lot.
So, that's a real long way of answering "It depends." You relly need a Realtor to take a look and give you his/her opinion.
Hope that helps.