Lots of people up North have a separate spa because they close their pools in the winter but want access to a spa in the winter. Not that you are up North, but my point is that it wouldn't look that odd to everyone. My take is this, do you want to be able to heat the pool at all? If so, the spa and smaller pool would be worth the investment. If you are just going to build the pool now without the propane and never be able to heat it think of the potential loss of use over the colder months. If you are ok with that, then I would say lose the spa and do the bigger pool. This probably isn't very helpful right? Sorry - just trying to help you think through it.

My 2 cents is buy cool deck. I am in Texas too, and it is hot to walk on anything that isn't grass or cool deck.

Also, pool spas don't have the same kind of comfy seats and all the adjustable jets that a morgan spa type spa has. I don't know how many months out of the year in Houston you would really WANT hot water. Maybe 4 or 5? My kids swim (unheated) at least 8 months out of the year.

I would think that a bigger pool would be better. We do use our spa quite often in the winter months, but we use the big pool almost every day once it's warm enough to wade in.
If you miss having a spa later, you can always buy a hot tub (and close it in the summer months like my neighbor). Since the heating is going to be a problem, that might be the best way to go anyway. We were lucky that we had gas to our house, oddly, just to the water heater in the garage (I suppose electric ranges were all the rage in 1970), which we extended into the house when we remodeled the kitchen and laundry room for a gas range and dryer, and now along the side of the house to the spa heater.
We have Artistic Pavers Shellock, which are pretty cool in the hot sun (compared to regular pavers) and expensive, but we end up using flip flops almost all the time anyway. We don't want to track grass or dirt into the pool and we need them for the shell under our tiki hut, so the deck isn't as important as I thought it would be.
We also got a removable hand-rail offset at the main steps that we thought would be for when in-laws visit, but we ended up never taking it out. We use it for hanging towels that we grab as we step out into our flip flops. The fact that it's off-set instead of smack in the middle of the steps is really great.
Anyway, biggest thing to think about is how YOU really expect to use the pool. If you are building it for your own young kids - remember they grow up fast you will be stuck with a pool you won't use for yourself once they're out of the house, so if YOU want a spa, get the spa.
I was warned off of building a pool by lots and lots of people who had them for their kids - but our pool was really for me, and now my hubby uses it more than I do! The teens and their friends are just a temporary bonus. And the salt system is so easy to maintain, a happy surprise.

I'm in CT, my pool is open from April to November.

While all of the kids and some of the adults that visit use our pool, everyone seems to use the spa.

As the action in the pool slows down, the spa becomes the gathering place.

When just adults are over, the spa is much more popular than the pool, especially when my wife has her friends over.

My pool is 20' by 40' with a side spa. We started out with a small 3' wide perimeter ribbon of Kool Deck around the pool, and a few years later we expanded the pool patio with about 1800 sqft of slate tile over concrete slab surrounding the pool and kool deck.

There are ways to "future proof" your layout and design so you can get a little now and more later.

At the time I wanted a 40' long pool for swimming laps. Matter of fact, I was swimming laps this morning. So when we made out our wish list, I went for pool size. Then we wanted the spa. We knew we eventually wanted a larger deck, but at installation we sacrificed on the initial deck size. Then we added a larger deck/patio a couple of years later.

I don't ever remember being inconvenienced by not having a large pool patio at first, even with young kids running all over.

This photo shows the original Kool Deck surrounded by the add-on patio:

I was reading this and curious as to what you decided on, I am also trying to decide on Spa or Larger pool?

I am in New England, some up here think a Attached Spa is a waste, I am dead set on getting one. My reason is I would not use it in the Winter (Most people do not) and to me it extends the season at least a few weeks on each end. If the pool is cold (I like it that way) you do not really care becuase you know you can just jump in the Spa that takes 15 minutes to warm up. Going back and forth with an attached Spa is much better than a seperate one and I do not really like the look of a stand alone Spa.

My husband wanted our pool to begin with. Growing up, I made friends with pools. My husband grew up having pools. So when we built ours, he didn't want a spa because they never used theirs growing up.

So, we didn't build a spa. In 2008, we built a 30K gallon pool with large shallow play area (27' long) and a diving pool. We did lots of agregate decking, a 12x12 rough red cedar arbor and grotto waterfall for 40K.

The last two winters, I wish we had had a spa and so do our teenagers. That said, we still use our big pool way more than we would ever use the spa. Being in TX, I don't think we would ever use a hot spa in summer. And the expense of it was that of a small pool.

Here's our pool sans spa

Good luck.