What if it had both? It's an imaginary book and this is just an exercise in constructive discussion. I do not think WotC is going to call me up and ask me how I would improve their game.
I'm actually surprised at how many of you have said "no."
It would depend on how much good the stronghold rules were. And I guess I could admit that if the boring stuff were too lengthy there might be some of that irrational purchaser-anger involved if I started to feel like I was paying extra for unwanted rules just to get the stronghold rules. Not sure that's 100% defensible, but you know how it is. Sometimes you can sell someone something for $40, but you can't sell them that same thing bundled with something they don't want for the same $40 because now they psychologically value it at less than $40 and resent the extra material they feel is pushing up the price.
Here's how I look at it:
When it comes to stuff like, "how much does a ten foot pole cost?" I seriously do not feel the need for rules. Not only do PCs tend to have huge amounts of purchasing power by mid levels, limiting the use of such material, but I just don't see the need for much granularity. Knowing that a ladder costs X, but a rope costs Y, is useful if you need to make decisions between which you can best afford. But you rarely need to do that in D&D, and if you wanted to make a game where that was necessary, you'd need to re-do the whole imaginary economy to reduce the growth in PC net worth over time. Or to put it another way, anyone who can buy a castle and run a stronghold doesn't have to price shop on rope.
And when it comes to things like "what are the exact stats of a donkey, and how much can it carry?" I don't feel the need for much detail because I can wing that just fine. In fact, if that came up in a game I'd probably feel a bit annoyed at having to look up the "right" answer when a "good enough" answer can be invented out of thin air.
Plus, its not likely that my players will look through a book of mundane gear and say, "Oh! I never thought of that!" They don't need ideas for this sort of stuff. They can come up with that on their own.
But a stronghold book? That's different. Chances are my players don't know how to design a functional castle. Plus there's a cool fantasy-play element in designing a castle, drawing maps, coming up with details like where the archers could be positioned, etc, etc. A castle or stronghold can also be something the PCs can be interested in all through their careers- at low levels, mundane construction and basic gear for a small fortified estate might be fun. At mid levels castles, and at high levels fancy magical upgrades or locales.
A stronghold book can add things that I can't invent off the top of my head, and that's why I think its so much more worthwhile than a book of basic gear, even if the presence of basic gear adds a sense of verisimilitude for some people.
