I don't see any issue with going to HO. It is a nice scale to run and the selections are almost limitless. A nice HO layout takes about as much space as an O layout as minimum recommended radius for HO used to be 36" (O72) equivalent. However in that same space you can run long consists of trains and they don't look out of place like they do on my layout. I enjoyed my HO days.
Good luck with whatever your decide!
Is that something the more detailed modelers in HO use as a guideline?
I recall the standard sectional track with 18" radius (36" diameter) was considered the normal minimum (though there were 15" radius curves available too, and I recall 22" radius being for larger engines). I was never into a serious level of modeling though, mostly sectional track and some flextrack here and there to either fit odd situations or remove track joints with a longer run of continuous rail.
I never was involved with any clubs or had any truly large models (had Bachmann N&W J's and a Niagara though) where a 36 inch radius would have been helpful or required.
This thought actually crossed my mind before reading your post. All of the references to 4 times the space don't count for the curves. It's true for straight runs of track and structure sizes, but an O Gauge O-31 circle fits inside an 18" radius circle of HO track. (well, maybe it's very close, but an O-27 loop certainly fits inside)
To answer the original question, I still have lots of HO from when I was a kid. The lack of accessories and operating cars (same exact thing as Art Young stated!) is one of the big factors that drove me to O once I was an adult and had the ability to get into it.
While I won't say I won't ever dust off the HO, I won't do it just to get a bigger layout. The more frequent derailments and such are not as enjoyable to me. I am sure with serious effort of laying cleaner track joints, adding weights to cars and making sure every car is also Kadee equipped can help, but it's a lot of extra effort.
-Dave