So in summary - I'm not going to get the router cutter I want ! And
should therefore invest in a spindle moulder ! Hmm - that's not
really an option is it? A round bead + V cutter is not recommended so
perhaps what I'm going to have to look at is a routed round bead and a
cutter for the moulding plane, possibly shaping the cutter myself. I'm
not really that enthusiastic about scratching.

In summary I'd say take the nearest match of router cutter to a saw
doctor and ask them to modify it to cut exactly the bead and sharp "v"
you want. (nb v is called a "quirk" in this situation). Only buy a
spindle if you are going in to mouldings in a biggish way - or if you
want total control of design and details.

I do suppose it's not possible to modify a router to do spindle
moulding ?

Router is essentially a tiny portable spindle moulder. Hence can do
same as spindle moulder but very limited size of cutters - small work
only. Spindle usually 30mm dia compared to router at 1/4inch or 1/2
inch, so tools not interchangeable. But some spindle moulders can take
router cutters in an add-on head attachment, if it has enough speed,
but max on SM is often about 8000rpm
cheers

Jacob