Miden, i also played a lot of 'old' songs with 'new' beats at gigs (particularly at restaurants). With a wide range of old and young customers, using the modern style routine you can cater for all age groups simultaneously. The old crowd enjoy it because they recognize the song, the young crowd enjoy it because they can relate to the beat, and also because they see the performer trying to modernize the sound.
I agree that a lot 70's songs fit the bill, and even older songs such as 'Summertime' and 'Stormy Weather' worked very well to this formula. As an added bonus it can extend the shelf life of some songs that may otherwise be wearing thin due to repetitive performance of the exact same arrangement every time.
In the end it certainly can't hurt to have a widen selection of modern styles available.
Kind regards,
Mark