The butter dish shape is certainly not a reproduction, nor is it a re-use of any of Imperial's earlier moulds. The butterdish is classed as Contemporary Carnival from the later production of Imperial (circa 1960s). The pattern most certainly IS a re-issue. The IG logo dates from that time.
Actually Imperial ceased
a decade before 1983. In the early 1970s it was sold to Lennox Inc. Logos on the glass from that era are LIG. Then in 1981 the company was sold to Arthur Lorch, and yet another logo appeared on the glass -ALIG. One more change before bankruptcy when it went to Robert Stahl, and the doors at the Imperial factory closed in 1985. There was a final flutter (Maroon & Pioneer Enterprises) for a couple of years, but then that was it.
Value? Ah well Christine has already pointed you to Dave's site. Values are a movable feast of course. Neither item is a big bucks piece, though.

But on the bright side, there are plenty of Imperial collectors and the butterdish, though newer, is possibly less available than the marigold water pitcher.