The job of Sundial of the Infinite is to break other cards. Tech that interacts is always emerging. Single printing. Cheap as bulk right now. Foils may not see another printing for a decade.
I'm fulling expecting Modern and Legacy decks to utilize this in a combo eventually.
I have no problem predicting that FOIL Sundials will see at least $10 within 18 months, if no other foil printing comes along.
You can't go wrong with these for under $0.50 apiece non-foil and $4.00 apiece foil. As you can see from the pricegraph, FOILs are seeing the bulk of the action at this point. Foils will see a stronger short-medium time-frame gain than non-foils.