Midi for me is a transit route - atlantic to med - visa versa - Ive done it so many time - however- a few interesting towns on route if you take the time to stop and look - first time i did it i didn't and wasn't that impressed - but over the years the likes of Castelnaudary, Toulouse, Bordeaux, Valence de Agen et.al. have grown on me plus the aqueducts at Agen and Moissac never fail to impress me - a bit messy on the southern side of the watershed but the Voi de Herault is a nice ride - and not stopping to poke around Carcassonne is a sin - on a nice sunny day it can be just wicked to toddle along in the sunshine on the tree lined banks - if you have never done it its a good starter tour - 3 days you don't get to smell the roses much
As to rivers in general and in particular Northern Europe - The flat European Northern Plain is a desert compared to the Midi - the rivers are where the interesting towns are - its a matter of stopping and bothering to look - the view of a tourist who cycles not a cyclist who tours and I make no apologies for that - the number of times I've spoken to people at campsites and asked "what did you think of so and so?" - to be told "oh we didn't stop"