I say buy a used Grom as there are hundreds of low mileage examples available. I've seen some great deals on these bikes that are still like new. Modified CT70's to the point of a grom have no real value to anyone but the owner. Once you start investing that much into a Honda CT70 you start seeing a hell of a lot better value in most any other form of transportation. Now fun value is measured on a completely different scale.
That there are so many recent model, low-mileage, examples available speaks volumes. Modified vehicles are NEVER worth much to anyone but their owners...one of the few constants in an ever-changing world. Your closing sentence, above, nicely restates what I said in my last post...the wise person chooses to suit his/her preferences.
When the MSX first hit the market, many months before it reached North America, I thought "oh boy, a new mini for over-aged kids. No more importing parts, upgrading shortfalls, etc". I also thought that it'd never be brought here and that the only way to get one was as a gray market import...back to the old conundrum of nothing under 450cc counting as a "real bike". That resulted in instantaneous overload of yet another bullshit detector, then back to square one...set a goal, then work toward its realization.
By the time the Grom reached the US of A and you could actually get one without waiting for months to pay a $1000-1500 "premium", the aftermarket parts set had begun catching-up. That left me cold. The Grom forums are populated mainly by younger guys who all "build" the same thing, cookie-cutter fashion. I'm kinda disappointed with the MSX engine and especially the alpha-n fuel injection. This is a cost-reduced engine, compared to the Wave/Nice series, never saw a big-bore Nice with a rod failure. There's still too little expertise with EFI for my liking and I've been through the "roll-your-own EFI solutions" thing, years ago...on the automotive side. (There are carburetor retrofit kits sold for the Grom...why is this if the EFI is ready for primetime?) It's about like asking to see the wine list at McDonalds, imo. That's okay, my generation was young, once, also. Still, I figured "okay, leave the driveline basically alone, go after the functional stuff...lame suspension, ball-buster seat". I could live with a similar power level, at lower rpm; it's still an OEM Honda motor and I loathe carburetors almost as much as breaker points. IOW, a more pedestrian version of what I'd already built.
The deal-breaker(s)...it'd cost me the same amount of money to bring a Grom up to the standard of my daily rider CT (well, ST70 frame actually) and this grumpy old man is old-school, not wild about the lines. Then, there's the versatility side or, more accurately lack thereof. The clincher, as if one was needed, was the insurance aspect. If my daily-rider CT custom is stolen, meteorite hits the garage, etc, the insurance company hands me $8K...agreed value coverage. That is not available for a new vehicle, period. After sciencing-out the process of upgrading the classic, the financial side actually favors it, over the newb model...somewhat of a letdown, not to mention surprise. That was shortsightedness, on my part; the Grom market is a much younger demographic and there are parallel comparisons to me made...used Hyabusa anyone? Ultimately, I discovered that I had already "out-Grommed the Grom". What's my motivation for going through the process of re-engineering the newer model?
Now, after all of that, you may think that I'm staunchly "two-thumbs-down" on the Grom. That would be an incorrect assumption. I am a bare-knuckled pragmatist. NEITHER machine is a one-size-fits-all solution to anything. Do this with your eyes wide open and sober-minded. Go in as well-informed as you can and don't expect to ever get your money back.
So, it ultimately boils down to building what you prefer. Either way, it costs what it costs.