"Is it worth adding a $500 Sbooster or IFI Elite to either the TT or phono or both?"
Too much audio forum/audio website reading and brainwashing.
Something like this. Look around and get without cartridge for $1500
Mobile Fidelity UltraDeck Manual belt-drive turntable with pre-mounted cartridge at Crutchfield
Schiit Audio: Audio Products Made in USA
Set it up, avoid audio forums and enjoy