I think it just depends on what you consider limited, and also who you ask.
You've already cited the main difference between X hacking vs. hacking for your Inc, and that's the locked bootloader.
From my current understanding all ROMs for the X have to be based off Motorola's original ROM(s) since only ROMs which have Moto's bootloader will run, otherwise it just won't work/boot/run/whatever. That also means you have to use the kernel that Motorola includes with their stock ROM. Normally on devices with unlocked bootloaders you can flash another kernel to change voltages and things like that, it's usually tweaked per battery life and stability.
Even though custom ROMs for the X are based off Motorola's originals, they are drastically different, especially from a GUI standpoint. The main two ROMs I've run, GummyJar and Liberty, are both without Moto's Blur and run beautifully. I also get better battery life on custom ROMs, not to say I didn't already get good battery before I rooted. I just always felt like Moto's Froyo Blur was slowing my DX down, and ROMs really set it free in so many ways, no more lag and better battery life.
Personally for me I've been able to do everything I've wanted, hacking-wise, with my DX. I know there are hacking purists out there who don't even want to bother with phones that have locked bootloaders. Though for my needs, the DX hacking scene has worked out fine. Especially now that there is a copy of Moto's Gingerbread, once the dev community gets working on Gingerbread ROMs we will see some great things.
You do mention you'd like the bigger screen and better battery life. How long does a normal charge last you on your Inc.? My DX lasts me through the day easily though I don't have much auto-syncing other that a few gmail accounts. I do use it moderately for other 3G data though.
Sorry if this post explains things you may already know, but I hope it helps!