For anyone to value this sign they would need to see the whole sign and have some idea of the measurements. I don't do evaluations so I'm no help there.
As for dating it.....definitely not 1970's! Mobil dropped the shield logo in 1955. With the serif or open A in Mobilgas it would predate 1945, and with the use of the progressive lines and red shield border I would be inclined to say it's actually from the early/mid 1930's, especially if the background color is more ivory and not white. It's hard to tell from the photo, at least to my eyes. It's not a sign I'm familiar with although I may have seen it in period photos and not taken mental note.