“Physically attending a particular place on a particular day of the year never really had too much significance.”
Uh, Meron on hilula diRashbi.
“do you think other Jews who DON’T go to Uman on RH are unable to get any sort of kedusha throughout their year?”
I think that’s precisely what they think, and thats why they do it. Well im sure there are similar opportunities like going to kivrei tzadikim or being connected to a tzadik. Anything wrong with them thinking that way?
” I suspect the “kedusha” you are referring to is simply inspiration derived by seeing so many Jews in one place.”
That too but not only that. Some might think they are on a spiritual high when its simply like you said but that doesnt detract from hashpaos being drawn down on the neshoma that they may not be aware of.