So let me get this straight...
The reface is not an accurate enough Rhodes emulation for you, but a Mellotron patch is? Despite it having absolutely no velocity response and one 'sample' per key?
And you want a hardware Mellotron despite your prior belief that software versions are now perfectly adequate replacements and you couldn't see the point in hardware versions?
And you're happy to drive a rack version over MIDI despite believing that MIDI latency is a problem?
The world turns in strange ways!

That Rhodes sound is available in Streetlytron Pro and in M-Tron's Streetly Tapes Vol 2. For me the latter is the better choice, but knowing you you'll disagree!

When I play my Mellotron sounds, no matter what is generating the audio, I tend to do so from my real Mellotron keyboard. That sets the key range without me having to think about it, and also gives me poly aftertouch like the real thing. To this end it's a shame that M-Tron has no PAT response, but I have my own way of dealing with that.
So if you want the real 'tron experience that's one thing, but you can't get that Rhodes sound in the hardware version natively.