I know where you're coming from - I particularly like "Time", and "Out Of the Blue" is almost a concept album. The (blue) vinyl has a superb cover, poster and space-ship cut-out!
Jeff Lynne, of course, cut his teeth in The Move, and was responsible for the far-out use of cellos and violins up front, rather than the typical "Spector" wall of sound strings. The Move are another band worth investigating, if you like ELO. Intelligent pop with a sense of humour - after the Beatles released "Strawberry Fields" and "Penny Lane", they responded with "Blackberry Way". Their hit "Flowers in the Rain" got them into trouble, after they tried to promote it with a postcard featuring Harold Wilson. He sued them, and the profits went to charity. The single was the first ever to be played on Radio 1 when it was launched (if I remember correctly!).
Cutting-edge, intelligent pop, definitely - but I don't think ELO can be considered prog. Witness "Discovery" and "Xanadu" - with Olivia Newton John!