This is such a good question!
For me - my personal opinion, not a judgement - I think that for a pilgrimage to be a pilgrimage one has to walk alone - meeting others along the way, yes, but essentially to be alone. Mainly because if one travels with a friend there is too much talking and not enough reflection, introspection.
Too much "what Sylvia/John would think about this .. oh yes, they should never have got divorced, I hear Stephen is applying for that new job, I hope the new boiler is installed when I return home, last winter was awful, oh, what a lovely church, a bit like the one we saw on our holiday last year in Bognor ..." sort of thing.
Whereas for the solitary pilgrim the foot journey is two-sided, the external physical journey being a mirror, or metaphor, of the internal spiritual journey.
Arriving at a sacred site by train/plane/boat/car, etc is a different thing - not somehow 'lesser' but different. Their 'journey' happens when they are there. The preparation and thinking about the shrine has been almost the same (?) but the inner process is done in a different way. Following the rites and rituals of the shrine is its own journey, both inner and outer and the destination, surely, is the same.
But I do think that the thing about solitary pilgrimage is also true for those who arrive by machine - it is a special thing, a special process - initiation into connection with other really - and if one is chattering away and taking photographs it is merely another holiday destination, not a pilgrimage to a sacred shrine.