Question I already own a Digitech Studio Vocalist. Is there anything to be gained by purchasing a VoicePrism, or VoicePrism Plus

The VP and VP+ have 24-bit digital resolution, as compared to the 16 bits in the Digitech. This results better fidelity and processing "headroom," consequently less-noticeable artifacts, lots of TC designed on-board effects, and four independent Gender units instead of two. The VP is a cool addition to a live gig because of the integrated effects, dynamics, phantom powered mic preamp, and digital I/O. For the Studio its a better and more flexible vocal channel than most project studios have, with the addition of all the extra control given by the effects. Furthermore the lead voice Physical Modeling is great for tweaking your voice and also coming up with new effects. As far as the standard - non-Plus - Voiceprism goes, its very popular with songwriters, project studios, remix people and also live musicians. Its very popular for live use because of the integrated effects, comp, EQ etc. For harmony control, there is Scale mode, Notes (MIDI control) mode and Chord mode (MIDI chord recognition is automatic and determines the best harmonies to fit the incoming MIDI notes). An innovative and unique feature in VoicePrism/VoicePrismPlus Chord mode allows the Bass voice to pedal over any chord as well as do inversions. The VoicePrism has the following additional differences from the Vocalists: the names of the four harmony types have been changed to Shift (Chromatic), Scale (Scalic), Chord (Chordal), and Notes ("Vocoder"). Gender is now independent on a per-voice basis, rather than having Gender Styles which in turn have only two Gender settings that can each be assigned to any of the four Harmony Voices. A powerful Mic Preamp is built-in, and effects include Chorus (thickening effect to turn your Mixed Quartet into the Mormon Tabernacle Choir, for instance), Flanging (special effect), more powerful Reverb, etc. You get two effects units, and they can be configured in series, parallel or series/parallel. The first effect block can create chorus, flange, and delay effects. The second block can create delay and reverb effects. The Delays (echoes) in the two Effects units, include simulations of old analog tape Delay units. Like the Studio but unlike any other Vocalist, the VoicePrism includes Timing, allowing for random delays of the actual generations of the notes sung by the voices, which can greatly aid realism since real singers never sing PRECISELY in sync.