I spend a fair amount of time walking the Thames footpaths from Shiplake down to Maidenhead ( NOT in one walk, I might add ! ) and I have to say that despite having polaroids AND binoculars with me I rarely see fish rising in any numbers....However, I do keep an eye on the many little streams entering the main river and when it's really quiet I have seen some decent shoals of roach holding up in the slow water at this time of year. Unfortunately they seem to do a disappearing act once the season opens !!
Downstream of weirs where shallows might occur also a good place to see very good fish holding station in the slower areas. ( Boulters Lock Island nr Maidenhead has a weir and is such a place BUT not with hoards of people around ! )
' Seeing ' is not catching, though.............................................
ps You will already know the stretches you mentioned are always very busy, what with boats, canoes and even swimmers, not to mention folk with kids feeding the ducks, so hardly conducive to fish rising in profusion along footpaths, BUT as I say, walk early morning or late evening may well show more .
Those little side streams are good though..
ps Some on FM do very well on the Thames in the Marlow area, but I cannot say more than that - nod, nod, wink, wink......