DSLR will allow more flexibility, but you mention you don't want to change lenses....although there are wide focal range zooms out there circa 18-200mm.
Keeping images purely on the monitor means ultimate image quailty will not be such a key factor between. Even on a projector I assume you can only show X x Y pixels, which will be alot less than camera is producing ?
I would say you can't justify the extra money for the DSLR over the powershot at this moment in time.....in my humble opinion
